UC-NRLF 


KBED,  Yf  ILL  I  AM  GATHER. 
FROST      I 


TK 


GIFT  ©F 


FROST  IN  THE  UNITED  STATES 


By 


WILLIAM  GARDNER  REED 

Meteorologist,  U.  S.  Weather  Bureau,  Washingtou,  D.  C. 


PAPER  PRESENTED  BEFORE  THE  SECOND  PAN  AMERICAN 

SCIENTIFIC  CONGRESS,  WASHINGTON,  U.S.A. 

DECEMBER  27,  1915— JANUARY  8,  1916 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 
1917 


i 


FROST  IN  THE  UNITED  STATES. 

By  WILLIAM  GARDNER  REED, 
Meteorologist,  U.  8.  Weather  Bureau,  Wastiington,  D.  C. 

INTRODUCTION. 

The  period  of  plant  growth  in  all  middle  latitude  countries,  such  as  the 
United  States,  is  limited  by  the  occurrence  of  low  temperatures.  Of  these  low 
temperatures,  killing  frost,  so-called,  probably  has  the  greatest  bearing  upon 
agriculture.  A  killing  frost  may  be  defined  as  a  low-temperature  condition 
which  is  so  injurious  to  plant  tissues  that  growth  is  no  longer  possible,  even 
when  the  low  temperature  has  passed.  The  limitation  of  plant  growth  by 
frost  is  different  from  that  due  to  lack  of  energy  sufficient  to  bring  the  plant 
to  maturity.  The  frost  limitation  results  from  the  definite  destruction  of  plant 
tissues,  and  in  most  cases  when  the  growth  for  a  single  year  is  injured  by  frost 
that  year's  crop  is  destroyed. 

THE    NATUBE   OF   FBOST. 

Frost  conditions  have  been  classified  under  three  headings:  (1)  The  com- 
mon hoar  frost;  (2)  the  dry  freeze  or  black  frost;  (3)  the  general  freeze. 
The  first  two  are  the  result  of  the  chilling  of  the  surface  air  by  rapid  radiation 
from  the  earth  to  space  and  are  essentially  local  conditions.  They  are  often 
the  result  of  widespread  controls,  but  the  temperature  in  each  locality  is 
mainly  the  result  of  local  radiation  conditions.  The  general  freeze  is  a 
condition  when  the  temperature  of  the  whole  mass  of  air  is  dangerously 
low.  The  general  freeze  is  not  the  result  of  local  conditions,  although  the  low 
temperatures  during  a  general  freeze  are  often  intensified  by  the  local 
radiation.1 

Prom  the  point  of  view  of  frost  damage  and  from  the  effects  on  vegetation 
of  these  low-temperature  conditions  the  Weather  Bureau  has  made  the  follow- 
ing classification : 

Light  frost. — That  which  has  no  destructive  effect,  although  tender  plants 
and  vines  in  exposed  places  may  be  injured. 

Heavy  frost. — That  in  itself  severer  than  a  light  frost ;  that  is,  the  deposit 
i>f  frost  is  heavier  and  the  temperature  falls  to  a  lower  point,  although  the 
staple  crops  of  the  locality  are  not  generally  destroyed. 

Killing  frost. — That  which  is  generally  destructive  of  vegetation  and  the 
staple  crop  of  the  locality.2 

The  character  of  frost,  whether  light,  heavy,  or  killing,  must  sometimes  be 
determined  by  the  phenomenon  itself,  rather  than  by  its  effect  on  vegetation  and 

1  Deals,  E.  A.  Forecasting  frost  in  the  north  Pacific  States.  U.  S.  Weather  Bureau 
Bui.  41,  Washington,  1912,  p.  41. 

8  U.  S.  Weather  Bureau,  Instrument  Div.,  Circular  B  and  C,  ed.  5,  Washington,  1915, 
p.  25. 

25807C-2— 17 1 


544J47 


2          PK<X)EED^:was.SE,cojTii  P.AN  AMERICAN  SCIENTIFIC  CONGRESS. 

the  staple  crops,  since  the  latter  may  ha\te  passed  the  state  where  injury  was 
possible.1 

It  should  be  noted  that  there  is  some  doubt  as  to  whether  the  reported 
frosts  correspond  very  closely  with  these  definitions.  It  is  probable  that  in 
many,  if  not  most,  parts  of  the  United  States  a  killing  frost  is  regarded  simply 
as  a  temperature  condition  \vhich  is  destructive  to  unprotected  garden  vege- 
tables. It  is  certain  that  hardy  grains  are  frequently  or  usually  not  killed  by 
temperatures  which  are  reported  as  killing  frosts.  Such  an  agricultural  classi- 
fication of  any  meteorological  phenomenon — and  the  occurrence  of  frost  must 
be  regarded  as  a  meteorological  phenomenon,  although  many  of  its  effects  are 
clearly  agricultural — is  unsatisfactory  because  it  depends  upon  the  opinion  of 
individual  observers  which  of  necessity  varies;  because  different  plants  are 
subject  to  different  amounts  of  damage  from  the  same  temperature  condi- 
tions; and  because  the  same  plants  are  not  equally  susceptible  to  damage  in 
different  stages  of  their  development.  However,  the  agricultural  significance 
of  thes£  temperature  conditions  does  rest  upon  the  damage  which  results  from 
the  temperature  conditions,  and  to  that  extent  at  least  an  agricultural  standard 
is  justified.  The  inconsistencies  in  recording  killing  frosts  are,  moreover,  not 
as  great  in  practice  as  they  would  be  if  all  observers  followed  strictly  the 
Weather  Bureau  definition.  There  are,  of  course,  many  stages  of  frost  damage 
and  whether  or  not  a  particular  frost  is  to  be  recorded  as  "  heavy "  or 
"killing"  is  largely  a  matter  of  opinion.  Many  frosts  are  clearly  killing  and 
many  are  clearly  not  killing,  but  the  frosts  which  have  the  greatest  agricul- 
tural bearing,  namely,  those  of  the  late  spring  or  early  fall,  are  often  on  the 
border  line  between  heavy  and  killing,  and  the  designation  of  these  frosts 
becomes  of  great  importance.  It  is  desirable,  therefore,  that  some  temperature 
condition  should  be  established,  if  possible,  which  corresponds  with  the  condi- 
tions of  killing  frosts.  This  unfortunately  has  not  been  the  case  so  far. 
although  Fassig  has  adopted  an  air  temperature  of  273°  A.  (32°  F.)  as  a 
better  indication  of  the  conditions  than  the  reported  killing  frosts  in  Mary- 
land. He  says : 

Some  of  the  reasons  which  may  be  advanced  in  favor  of  the  method  of  deter- 
mining the  period  from  the  temperature  records  are  the  following: 

1.  The  temperature  is  observed  and  recorded  regularly  each  day,  and  the 
record  is  therefore  complete  for  the  entire  season. 

2.  Frost  records  are  apt  to  be  incomplete  unless  they  occur  at  critical  periods 
In  plant  growth.     This  failure  to  record  frosts  is  particularly  noticeable  in 
records  of  spring  frosts;  stations  having  excellent  fall  records  have  often  a 
very  defective  record  of  spring  frosts.     Frosts  occurring  after  a  long  period 
of  warm  weather,  as  in  summer  or  early  fall,  are  likely  to  be  more  conspicu- 
ous events  than  the  last  of  a  series  of  many  frosts  occurring  throughout  the 
winter  and  early  spring. 

3.  In  recording  frosts  there  is  always  a  variable  personal  factor,  opinions 
differing  as  to  the  extent  and  severity  of  the  frost,  resulting  in  the  same  frost 
being  designated  as  "  heavy  "  or  "  killing."    In  recording  temperatures,  on  the 
other  hand,  this  personal  factor  is  practically  eliminated. 

4.  There  is  a  fairly  fixed  and  uniform  relation  existing  between  the  tempera- 
ture in  the  shelter  and  the  occurrence  of  a  killing  frost  in  any  given  locality, 
and  this  factor  can  be  readily  determined  from  a  comparatively  short  series  of 
observations. 

5.  For  reasons  stated  above  a  reliable  "  frostless  period "  may  be  estab- 
lished for  a  given  locality  from  a  shorter  series  of  observations  by  the  use  of  a 
temperature  record  than  by  the  use  of  a  frost  record/ 

1U.  S.  Weather  Bureau;  Instructions  for  preparing  meteorological  forms,  ed.  1915, 
Washington,  1914,  p.  11. 

2  Fassig,  O.  L. :  Period  of  safe  plant  growth  in  Maryland  and  Delaware  [U  SI 
Monthly  Weather  Review,  42  :  152-158,  Washington,  1914,  p.  152. 


ASTRONOMY,  METEOROLOGY;  AKI>  SE^MOL20GY'.  :  3 

In  practice  many  of  the  frost  data  used  of  the  maps  presented  with  this 
paper  have  been  determined  by  the  occurrence  of  freezing  temperatures.  There 
is  a  varying  difference  in  temperature  between  the  ground  and  the  air  at  the 
height  of  the  instrument  shelter,  which  depends  upon  a  great  variety  of  condi- 
tions, among  which  are  the  state  of  the  sky,  the  humidity  (perhaps  the  amount 
of  water  vapor  is  more  important  than  the  relative  humidity),  the  air  move- 
ment, and  the  length  of  the  night.  But  as  the  controls  are  also  the  controls 
of  frost,  Fassig's  statement  holds  in  most  cases. 

If  an  agricultural  standard  is  used  for  the  determination  of  frost,  it  will  be 
found  that  these  low  temperatures  are  of  the  greatest  concern  to  agriculture  at 
times  when  the  crops  are  in  a  condition  to  be  damaged.  The  probable  occur- 
rence of  such  damaging  conditions  limits  the  availability  of  different  portions 
of  the  United  States  as  agricultural  regions,  and  a  knowledge  of  these  condi- 
tions will  prevent  many  agricultural  failures.  The  portions  of  the  United 
States  in  which  freezing  temperatures  are  not  of  annual  occurrence  are  very 
limited.  These  are  a  part  of  the  peninsula  of  Florida,  the  immediate  Gulf  coast, 
and  a  small  area  in  southern  California  and  Arizona.  In  so  far  as  these  con- 
ditions are  regular  and  not  extended  beyond  the  usual  time  of  occurrence, 
they  are  not  to  be  feared ;  this  is  a  period  of  plant  inactivity,  herbaceous  plants 
are  not  above  the  ground,  and  trees  are  dormant.  Except  for  the  regions  men- 
tioned, frost  damage  during  the  winter  is  not  important.  It  is  only  the  rare 
occurrence  of  extremely  low  temperatures  which  results  in  winter-killing,  and 
this  is  an  entirely  distinct  phenomenon,  not  to  be  confused  with  frost  damage. 

FEOST    RECORDS. 

In  the  United  States  frost  is  of  agricultural  significance  in  different  regions 
at  different  times.  In  the  region  of  the  citrus  fruits — that  is,  Florida,  the 
Gulf  coast,  and  southern  California — frost  damage  will  occur  whenever  the 
fruit  is  on  the  trees,  provided  the  temperature  falls  a  few  degrees  below  freez- 
ing. Slightly  lower  temperatures  are  necessary  to  damage  the  trees,  but  the 
general  statement  that  any  freezing  temperature  is  dangerous  in  the  citrus 
region  is  not  far  from  correct.  Outside  the  citrus  region  winter  frosts  are  of 
very  little  importance ;  it  is  the  spring  and  fall  frosts  which  become  of  interest 
to  agriculture.  Deciduous  fruit  trees  are  dormant  during  the  winter;  low 
temperatures  are  to  be  feared  only  after  growth  has  commenced.  The  time 
of  danger  from  frost  to  the  deciduous  fruits  is  the  time  between  the  opening 
of  the  buds  and  the  picking  of  the  fruit.  Of  course,  during  a  great  deal  of  this 
time  the  temperature  conditions  are  such  that  frosts  do  not  occur  in  regions 
where  fruit  is  grown.  The  period  of  anxiety  is,  therefore,  limited  to  the  begin- 
ning and  the  end  of  the  season  of  plant  activity ;  that  is,  from  the  opening  of 
the  buds  to  the  setting  of  the  fruit  in  the  spring  and  the  period  just  before 
picking  in  the  autumn.  Other  crops  than  fniit  are  subject  to  varying  amounts 
of  damage  by  frost.  Temperatures  not  many  degrees  below  freezing  are 
destructive  to  most  crops  except  the  hardy  grains,  and  successful  agriculture 
can  not  be  carried  on  except  in  regions  where  the  time  between  the  last  killing 
frost  in  spring  and  the  first  killing  frost  in  autumn  is  as  long  or  longer  than 
the  normal  period  of  growth  required  by  the  plants. 

The  agricultural  importance  of  frost  data  can  hardly  be  overemphasized, 
since  the  character  of  the  farming  in  any  region  is  .dependent  upon  the  time 
between  killing  frosts.  This  does  not  mean  that  the  time  between  killing  frost 
is  the  only  consideration,  but  that  the  period  available  for  plant  growth  is 
limited  to  this  time.  There  are  often  other  limiting  conditions,  such  as  lack 
of  heat  in  sufficient  amounts  to  permit  plants  to  reach  maturity.  These  other 


PROCEEDINGS.  -SECOND  FA-N  AMERICAN   SCIENTIFIC   CONGRESS. 


conditions  may  prevent  the  growth  of  all  the  crops  which  would  appear  possible 
from  the  length  of  the  season  between  killing  frosts,  but  the  length  of  the 
season  is  to  be  regarded  as  a  very  important  and  very  definite  limitation.  It 
is,  of  course,  possible  to  protect  crops  from  frost  damage,  but  this  protection 
can  profitably  be  carried  on  only  within  very  narrow  limits.  Protection  is 
always  obtained  at  considerable  expense,  and  unless  applied  to  a  high-value 
crop  is  seldom  justified  by  the  returns.  Thus  protection  from  damage  by  frost 
is  to  be  regarded  as  a  type  of  the  most  intensive  methods  of  cultivation,  which 
can  profitably  be  resorted  to  only  for  such  crops  as  fruits  and  vegetables  where 
the  value  is  concentrated  and  where  the  profits  from  cultivation  out  of  the 
natural  season  or  out  of  the  natural  region  are  great.  As  a  type  of  cultivation 
out  of  the  natural  season,  various  garden  vegetables  grown  particularly  in  the 
spring  may  be  noted,  and  the  extension  of  orange  culture  into  colder  regions 
is  a  good  example  of  a  type  of  production  out  of  a  natural  region.  Both  of 
these  types  of  extension  are  apt  to  enlarge  the  profits;  vegetables  reaching  the 
market  early  command  high  prices,  the  best  oranges  are  grown  at  the  very 
limits  of  the  possible  orange  regions,1  but  it  is  only  in  such  conditions  as  these 


RECORD  KILL!  NO 
FPOSTAFTER 
MAY  I  -  SZZZS 

APR.I5-  ??75&n 
APR.  !  -  E5S3 
MAR  IS-  V/SSS* 
MAR.  I  -  fX?^1 
ALL  FROSTEZHD 


FIG.  1.— From  U.  S.  Weather  Bureau:  Instructions  for  preparing  meteorological  forms. 

that  frost  protection  is  at  all  justified.  It  must  be  looked  upon  as  an  insurance 
charge  which  the  crop  must  carry  in  addition  to  its  value,  and  only  increased 
profits  can  justify  this  charge.2 

•  THE  OCCURRENCE  OF  FROST  IN  THE  UNITED  STATES. 

Except  in  a  limited  region,  frost  is  an  annual  phenomenon  throughout  the 
United  States.  The  length  of  the  season  between  the  last  killing  frost  in  spring 
and  the  first  killing  frost  in  fall  decreases  within  increasing  latitude.  Figure  1 
shows,  in  a  general  way,  the  conditions  of  spring  frost.  This  map  was  prepared 
by  the  Weather  Bureau  as  a  guide  to  its  officials  in"  recording  frosts  in  the 

1  Colt,  J.  E.    Citrus  fruits,  N.  Y.,  Macmillan,  1915,  p.  25. 

*  See  Reed,  W.  G. :  Protection  from  damage  by  frost.  Geographical  Review  1  •  130-122, 
New  York,  1916. 


ASTRONOMY,   METEOROLOGY,  AND   SEISMOLOGY.  5 

spring.  It  is  intended  that  the  last  killing  frost  in  any  year  shall  be  recorded 
by  each  regular  Weather  Bureau  station.  It  is  not,  however,  desired  to  record 
frost  every  day  during  the  winter.  The  map,  therefore,  represents  a  compromise 
between  these  two  ideas.  The  most  significant  thing  about  this  map  is  the  fact 
that  it  shows  clearly  that  while  the  last  killing  frost  in  spring  along  the 
Gulf  coast  and  in  California  may  occur  at  any  time,  the  date  of  this  last  frost 
becomes  later  and  later  until  in  a  considerable  portion  of  the  country  there  is 
little  or  no  possibility  of  the  last  killing  frost  occurring  before  May  1.  In 
the  fall  the  problem  is  simpler,  as  the  dates  of  light  and  heavy  frosts  are 
recorded,  and  that  of  the  first  killing  frost  only,  after  which  no  frost  is  recorded. 
The  temperatures  dangerous  to  growing  plants — that  is,  temperatures  which  are 
recorded  as  killing  frosts — are  usually  those  associated  with  the  types  known 
as  "hoar  frost"  and  "black  frost."  The  "general  freeze,"  which  is  a  winter 
weather  type,  and,  although  not  usually  found  at  the  beginning  and  end  of  the 
warmer  season,  is  occasionally  destructive  to  plants  in  the' spring  or  fall. 

The  frost  conditions  of  spring  and  fall  are  mainly  the  result  of  local  nocturnal 
cooling  under  the  clear  sky  conditions  accompanying  anticyclones.  The  weather 
conditions  which  precede  and  accompany  frost  in  the  various  sections  of  the 
United  States  are  closely  associated  with  the  progressive  movement  of  these 
areas  of  high  pressure.  East  of  the  Rocky  Mountains  the  general  movement 
of  these  anticyclones  is  from  the  northwest  to  the  southeast.  As  a  rule  the 
area  in  which  frost  occurs  is  southeast  and  a  little  in  advance  of  the  area 
of  high  pressure. 

It  is  frequently  possible  to  follow  the  advance  of  frost  conditions  across  a 
large  portion  of  the  eastern  United  States.  The  frost  probability  is  successively 
transferred  eastward  with  considerable  overlapping  of  the  areas  visited  by 
frost  from  day  to  day.  Generally  the  eastern  portion  of  the  area  visited  by 
frost  one  day  will  receive  a  second  visitation  on  the  following  day.  Studies 
of  the  occurrence  of  frost  by  the  forecast  officials  of  the  Weather  Bureau  are 
grouped  about  the  anticyclone  as  a  unit  rather  than  about  any  geographical  dis- 
trict, since  frost  may  occur  from  rather  widely  varying  conditions  of  the 
cyclone  with  respect  to  any  particular  district.1 

Frost  west  of  the  Rocky  Mountains  may  be  regarded  as  a  somewhat  simpler 
problem  than  that  in  the  eastern  United  States.  Frost  forecasting  in  the 
Pacific  Northwest  has  been  adequately  discussed  by  Beals.2  In  the  Pacific 
Northwest  frosts  are  intimately  associated  with  the  existence  of  an  anti- 
cyclone over  the  states  of  Washington,  Oregon,  and  Idaho.  The  extension  of 
this  anticyclone  over  the  Pacific  Ocean  seems  to  make  very  little  difference  as 
long  as  a  portion  overlies  the  land.  In  other  words,  the  transfer  of  air  from 
the  continent  toward  the  ocean  seems  to  be  of  relatively  little  importance. 
This,  however,  is  not  the  case  with  the  occurrence  of  frost  in  California. 
While  there  are  numerous  minor  variations  of  the  frost  type  for  California 
and  Nevada,  the  essential  features  of  this  weather  type  are  exceedingly  simple. 
An  anticyclone  overlies  some  portion  of  the  Basin  Region  accompanied  by  the 
usual  outflowing  winds.  This  gives  the  State  of  California  easterly  and  north- 
•easterly  winds  for  24  to  36  hours  before  frost  occurs.  Under  these  conditions 
the  air  is  apt  to  be  clear  and  dry,  and  often  a  great  deal  of  cold  air  has  been 
transferred  from  the  colder  continental  interior.  As  long  as  the  wind  con- 
tinues to  blow  this  air  will  usually  be  so  well  mixed  that  local  radiation  will 

1  The  writer  is  indebted  to  the  forecast  officials  of  the  U.  S.  Weather  Bureau  for  this 
statement  of  frost  occurrence. 

2  Beals,  E.  A. :  Forecasting  frost  in  the  north  Pacific  States,  U.   S.  Weather  Bureau. 
Bui.  41,  Washington,  1912. 


6  PROCEEDINGS  SECOND  PAN  AMERICAN   SCIENTIFIC   CONGRESS. 

not  be  able  to  effect  much  further  cooling,  but  if  the  wind  falls  off,  cooling  by 
night  becomes  of  the  utmost  importance.1 

The  fact  that  frost  conditions  are  generally  associated  with  anticyclones  is 
of  great  agricultural  significance.  The  anticyclone  is  characteristically  ac- 
companied by  clear  weather;  in  fact,  frost  conditions  are  essentially  those  of 
clear  nights.  The  same  atmospheric  conditions  which  result  in  clear  frosty 
nights  are  also  those  of  bright  sunny  days,  so  that  days  somewhat  warm  for 
the  season  frequently  occur  at  the  same  time  as  nights  with  frost.  These 
days  encourage  the  plants  to  carry  on  their  activities  of  growth  with  the  result- 
ing new  and  tender  tissues.  With  the  rapid  nocturnal  cooling  by  radiation 
from  the  plant  and  from  the  lower  air,  the  plant  juices  are  apt  to  be  frozen 
and  the  plants,  especially  the  new  tissues,  are  often  damaged.2 

FROST     DAMAGE. 

The  mechanism  of  frost  damage  is  complicated  and  not  very  well  understood. 
The  following  general  discussion  shows  the  present  state  of  knowledge : 

Once  it  was  supposed  that  frost  injuries  were  due  directly  to  the  formation  of 
ice  in  the  cells;  the  expansion  of  water  in  freezing  was  thought  to  burst  the 
cell  walls,  just  as  it  bursts  the  water  pipes  in  our  houses  in  severe  weather. 
This  plausible  theory  was,  however,  disproved  by  examination  of  freezing  plant 
tissues  under  the  microscope.  The  process  that  ordinarily  occurs  is  this : 

Ice  forms  not  in  but  between  the  cells,  and  in  so  doing  gradually  extracts 
the  water  from  the  latter  through  the  cell  walls.  There  are  two  ways  in  which 
this  loss  of  water  may  kill  the  protoplasm  of  the  cell,  and  opinions  are  still 
divided  among  plant  physiologists  as  to  which  is  the  more  important  one. 

The  belief  that  was  generally  entertained  a  few  years  ago  was  that  the 
desiccation  of  the  cell  contents  caused  a  collapse  of  the  protoplasm,  and  that 
whether  or  not  this  collapse  was  permanently  injurious  depended  especially 
upon  whether  the  water  was  all  restored  to  the  cell  in  the  subsequent  thaw. 
If  the  temperature  rose  gradually  the  water  would  have  time  to  soak  back 
through  the  cell  wall,  and  the  protoplasm  would  resume  its  normal  condition. 
In  a  rapid  thaw  the  cells  would  not  be  able  to  take  up  the  water  as  fast  as  it 
was  furnished,  much  of  the  water  would  escape,  and  the  structure  of  the  proto- 
plasm would  be  permanently  broken  down  and  destroyed. 

A  more  recent  view  is  that  the  injury  is  purely  chemical ;  the  loss  of  water 
causes  a  concentration  of  the  salt  solutions  in  the  cell,  and  these  attack  and 
"precipitate"  the  proteins — a  process  too  complicated  to  explain  here  in  detail. 
Suffice  it  to  say  that,  according  to  this  view,  the  death  or  survival  of  the  tissues 
depends  upon  the  length  of  time  the  concentration  of  the  cell  sap  continues  and 
not  upon  the  rate  of  subsequent  thawing. 

We  have,  then,  two  rival  theories  of  frost  injury:  According  to  one  the 
damage  is  done  chiefly  after  the  actual  freezing  is  over,  and  may  be  avoided 
if  the  temperature  rises  slowly ;  according  to  the  other  the  injury  occurs  during 
the  frozen  state,  and  depends  upon  the  duration  of  that  state. 

Perhaps  horticultural  writers  have  generally  laid  too  much  emphasis  upon  the 
importance  of  gradual  defrosting.  Thus  it  has  been  commonly  stated  that  wind- 

1  See  McAdie,  A.  G. :  Frost  fighting,  U.  S.  Weather  Bureau  Bui.  29,  Washington, 
1900 ;  "  Frost "  in  the  Climatology  of  California,  U.  S.  Weather  Bureau  Bui.  L :  227-237, 
Washington,  1903 ;  and  elsewhere. 

'For  more  detailed  statements  of  the  conditions  under  which  frosts  occur  see  U.  S. 
Weather  Bureau  :  Weather  forecasting  in  the  United  States,  pp.  177-215,  Washington, 
1916. 


ASTRONOMY,   METEOROLOGY,  AND   SEISMOLOGY.  7 

breaks,  covers,  and  other  devices  to  shield  buds  or  blossoms  from  the  direct  rays 
of  the  rising  sun  after  a  night  of  frost  will,  unless  the  frost  has  been  very 
severe,  save  the  fruit  by  preventing  a  too  rapid  rise  of  temperature.  A  certain 
amount  of  evidence  recently  accumulated  throws  some  doubt  upon  the  necessity 
for  such  precautions.  For  example,  during  the  frost  of  December  26,  1911,  in 
southern  California,  when  several  million  dollars'  worth  of  citrus  fruit  was 
damaged,  it  is  stated  that  at  one  point  the  temperature  rose  24°  in  two  hours 
without  injury  to  the  fruit.  The  results  of  experiments  made  by  the  Bureau 
of  Plant  Industry  in  a  cold-storage  warehouse  where  oranges  were  allowed  to 
thaw  out  under  various  conditions  after  having  been  kept  at  low  temperatures 
are  reported  as  follows : 

The  length  of  time  the  fruit  remains  in  a  frozen  condition  has  a  very  material 
effect  upon  its  condition  after  thawing  out.  There  is  apparently  an  optimum 
temperature  for  thawing  the  frozen  fruit  with  the  least  resultant  injury.  If 
the  thawing  is  done  too  slowly  the  fruit  is  injured  more  than  where  a  some- 
what higher  defrosting  temperature  is  used  and  the  thawing  accomplished 
more  quickly.  On  the  other  hand,  it  was  found  that  quick  defrosting  was 
more  injurious  than  slow  defrosting,  so  that  it  appears  probable  that  through 
experiment  the  defrosting  temperature  which  would  be  most  effective  could 
be  determined. 

In  other  words,  both  the  duration  of  the  frozen  state  and  the  rate  of 
defrosting  are  important  in  determining  the  fate  of  the  fruit;  but  while  slow 
defrosting  is  desirable,  it  should  not  be  too  slow.  It  is  assumed  here  that 
what  applies  to  the  mature  fruit  of  the  cold-storage  experiments  also  applies 
to  the  earlier  stage  of  bud  and  blossom,  though  in  the  latter  case  the  process 
is  doubtless  complicated  by  the  effects  of  cold  upon  the  fertilization  of  the 
ovary  and  the  consequent  setting  of  the  fruit. 

Evidently  much  more  investigation  is  needed  "concerning  the  nature  of  frost 
effects  within  the  plant.  However,  there  appears  to  be  at  least  one  practical 
corollary  to  the  foregoing  information:  Even  if  orchard  heating  has  been 
delayed  until  after  freezing  temperatures  have  set  in  there  may  still  be  time 
to  save  the  fruit.  The  utility  of  any  information  that  may  be  gained  in  regard 
to  the  ideal  conditions  of  defrosting  is  problematical,  for  it  is  not  easy  to 
see  how  such  knowledge  could  generally  be  applied  in  the  orchard. 

Now,  we  come  to  the  important  subject  of  frost  resistance.  Here,  also, 
much  work  remains  to  be  done,  and  it  is  the  duty  of  the  practical  horticul- 
turist as  well  as  the  scientist  to  help  in  the  common  cause. 

Comparatively  little  information  has  been  collected  so  far  as  to  the  tem- 
peratures that  various  species  and  varieties  of  cultivated  plants  will  endure 
for  an  indefinite  period  without  injury.  Such  information  can,  at  best,  be 
stated  only  in  averages,  because  in  the  case  of  a  given  variety  its  ability  to 
withstand  cold  depends  somewhat  upon  the  weather  conditions  previous  to 
the  freeze.  Thus,  as  has  been  pointed  out,  a  few  days  of  warm  weather, 
together  with  an  ample  supply  of  soil  moisture,  will  cause  the  newly  formed 
cells  of  the  blossoms  and  fruits  to  be  filled  with  a  watery  protoplasm,  or  cell 
sap,  which  freezes  more  readily  than  concentrated  cell  sap. 

Moreover,  individual  plants  of  the  same  variety,  grown  under  apparently 
identical  conditions,  vary  somewhat  in  their  resistance  to  cold.  Nevertheless, 
average  statements  on  this  subject  are  exceedingly  valuable,  because  the 
orchardist  is  chiefly  interested  in  knowing  what  will  happen  in  the  long  run, 
in  the  orchard  as  a  whole,  and  need  not  concern  himself  with  sporadic  cases. 


8  PROCEEDINGS   SECOND   PAN   AMERICAN   SCIENTIFIC   CONGRESS. 

An  authority  gives  the  following  table  showing  the  temperatures   (Fahren- 
heit) injurious  to  fruit  at  various  stages. 


In  bud. 

1 
In       i    In  set- 
blossom,  ting  fruit. 

At  other 
times. 

Almonds                                                                                            i            28 

I 
30                30 

28 

Apples                                                                                                            27 

29  j              30 

25 

Apricots                                                                                                 |             30 

31  i              31 

30 

Cherries.                                   29 

30  I             30 

29 

Peaches                                                                                                      29 

30  1             30 

28 

Pears  i            28 

29  i              29 

28 

Plums                                                                                                             30 

31                31 

29 

Prunes  30 

31                31 

29 

The  first  column  refers  to  buds  about  ready  to  open.  In  their  earlier  stages 
buds  can,  of  course,  stand  far  lower  temperatures.1 

THE  FKOST  DATA  OF  THE  UNITED  STATES. 

The  records  of  frost  occurrence  in  the  United  States  are  numerous,  although 
not  as  complete  as  might  be  wished.  There  are  records  three  years  or  more  in 
length  for  nearly  5,000  stations;  these  records  have  been  made  under  the 
direction  of  the  Weather  Bureau  and,  taken  altogether,  are  a  mass  of  data  of 
inestimable  value.  Of  these  5,000  or  more  records,  there  are  about  700  which 
have  been  continued  for  more  than  20  years.  These  data  have  made  possible 
the  compilation  of  maps  of  the  dates  of  frost  occurrence  over  the  eastern 
United  States.1 

Where  the  stations  at  which  frost  is  recorded  are  located  near  one  another 
the  official  data  are  sufficient  to  enable  isochronal  lines  to  be  drawn  with  con- 
siderable accuracy,  especially  if  the  region  is  not  one  of  broken  topography. 
This  is  the  condition  to  be  found  in  much  of  the  eastern  United  States,  and 
it  is  probable  that  the  addition  of  new  data  will  make  possible  only  minor 
improvements  in  the  lines  already  drawn  for  this  region.  In  a  mountainous 
region  such  as  the  western  United  States,  however,  the  condition  is  quite 
different.  Here  stations  are  widely  separated,  and  there  are  often  high  moun- 
tains or  deep  canyons  between  stations  relatively  near  together,  so  that  the 
conditions  at  the  stations  are  in  many  cases  only  local.  A  further  difficulty 
arises  from  the  fact  that  most  of  the  stations  in  the  western  United  States  are 
located  in  the  more  favored  places  where  farming  is  possible,  rather  than  in 
places  which  may  be  regarded  as  characteristic  of  the  whole  region.  It  is, 
therefore,  necessary  to  supplement  the  recorded  dates  of  frost  by  other  data 
unfortunately  less  subject  to  statistical  treatment.  These  data  are  topography 
and  records  of  crops  and  natural  vegetation.  The  hardiness  of  many  types  of 
vegetation  is  known  rather  accurately,  and  a  study  of  the  vegetation  which  is 
able  to  maintain  itself  in  any  particular  region  gives  a  good  idea  of  the  char- 
acter of  the  temperature  conditions.  It  is  also  true  that  altitude  has  an  impor- 
tant effect  on  temperature.  The  last  killing  frost  in  spring  becomes  later  with 


1  Frazer,  Calvin  :  The  frost  problem  up  to  date.  Country  Gentleman,  79  :360.  Phila- 
delphia. 1914. 

In  this  connection  see  also  Chandler,  W.  H. :  The  killing  of  plant  tissue  by  low  tempera- 
ture. Missouri  Agr.  Exp.  Sta.  Research  Bui.  8,  Columbia,  1913. 

a  See  Greeley,  A.  W. :  American  Weather,  New  York,  Dodd,  Mead  &  Co.,  1883,  charts 
22-23  ;  Day,  P.  C. :  Frost  data  of  the  U.  S.,  U.  S.  Weather  Bureau  Bui.  V,  Washington, 
1911  ;  also  Reed,  W.  G.,  and  Feldkamp,  C.  L. :  A  selected  bibliography  of  frost  in  the 
United  States,  U.  S.  Monthly  Weather  Review,  43  :  512-517,  Washington,  1915. 

A  new  series  of  frost  maps  will  appear  in  the  Atlas  of  American  Agriculture  now  in 
preparation  by  the  United  States  Department  of  Agriculture. 


ASTRONOMY,  METEOROLOGY,  AND  SEISMOLOGY.  9 

increasing  elevation,  other  things  being  equal,  and  the  first  killing  frost  in  fall 
becomes  earlier. 

Therefore,  these  data  may  be  used  to  supplement  the  official  records  where 
'  the  stations  are  far  apart  or  not  well  situated,  but  only  when  they  are  wisely 
and  conservatively  used,  especially  as  slope  and  the  presence  of  valleys  often 
result  in»  local  warm  and  cool  spots  not  dependent  upon  the  altitude.  It  should 
be  very  clearly  noted,  moreover,  thal^it  is  exceedingly  easy  to  make  inaccurate 
use  of  data  other  than  the  official  record  of  a  well-conducted  climatological 
service.  In  practice  it  has  been  deemed  best  to  map  at  the  proper  location 
the  frost  da.ta  reported  by  the  Weather  Bureau  and  to  consider  these  records 
as  of  primary  importance.  No  record  has  been  neglected  except  those  of  a 
few  stations  reported  by  the  section  directors  of  the  Weather  Bureau  as  un- 
reliable records  or  stations  with  extremely  local  conditions,  and  in  cases  of  ap- 
parent conflict  between  the  record  and  the  botanic  or  topographic  data  the 
record  has  been  followed.  The  exact  course  of  the  isograms  between  stations 
has,  moreover,  been  determined  by  all  the  data  available,  which  include  topo- 
graphical, botanical,  and  agricultural  material,  as  well  as  the  Weather  Bureau 
records.  Frost  data  for  selected  stations  with  longer  records  are  given  in 
Table  I.  These  stations  represent  a  fair  sample  of  the  frost  conditions  in  the 
country.  More  extended  frost  data  can  be  found  in  Bulletin  W  of  the  Weather 
Bureau.1 

While  the  actual  record  of  the  occurrence  of  frost  dangerous  to  crops  is  the 
best  guide  at  a  particular  station,  th-3se  data  become  so  numerous  that  it  is 
not  possible  to  use  them  for  wide  areas.  For  a  particular  station  in  a  given 
year  it  is  probably  essential  to  know  only  the  last  date  in  spring  and  the  first 
date  in  fall  on  which  killing  frosts  have  occurred  in  each  year.  For  a  series 
of  years  and  for  many  stations  these  data  become  hopelessly  numerous,  and 
some  statistical  method  of  reducing  the  number  of  dates  without  destroying 
the  value  from  the  longer  periods  covered  must  be  devised.  The  simplest  of  all 
such  methods  is  that  of  averaging  the  dates.  It  is  perfectly  possible  to  deter- 
mine the  "  average  date  of  last  killing  frost "  in  spring  by  simple  arithmetical 
methods.  The  date  thus  obtained  is  that  on  or  before  which  the  last  killing 
frost  has  occurred  in  about  half  the  years  for  which  there  is  a  record.2 

The  "  average  date  of  the  first  killing  frost "  in  fall  may  be  similarly  ob- 
tained. The  average  length  of  the  season  without  killing  frost — that  is,  the 
time  available  for  plant  growth,  provided  the  whole  season  can  be  used — may 
best  be  obtained  by  the  difference  between  the  average  spring  date  and  the 
average  autumn  date. 

1  United  States  Weather  Bureau,   Summary  of  the  climatological  data  of  the  United 
States,  by  sections,  Washington,  1912. 

2  Strictly   speaking,   the   median   date  is   that  before  which  the  last  killing  frost  has 
occurred  in   half  the  years.     However,  a  count  of  823  cases   shows   that  404  occurred 
before  the  average  date,  396  after  the  average  date,  and  23  on  the  average  date.     The 
median  and  the  average,  therefore,  fall  on  the  same  date.     This  is  the  case  when   the 
distribution  of  the  dates  follows  the  normal  curve  in  which   the  average,   the  median, 
and  the  mode  coincide. 


10  PROCEEDINGS  SECOND  PAN   AMERICAN   SCIENTIFIC   CONGRESS. 

TABLE  1. — Summary  of  frost 


Station. 
1 

County. 
2 

Alti- 
tude. 

3 

Last  killing  frost  in  spring. 

Years 
of 
rec- 
ord. 

4 

Average 
date. 

5 

Latest  date. 

9-10 

years. 

6 

1895-1914. 

7 

Since  be- 
8 

Alabama: 

Conecuh 

126 
125 

125 

37 

23 
33 

126 
27 
32 
26 
26 

43 
26 

30 
42 
28 

121 

59 
35 

25 
24 

133 
121 

126 
59 
23 

123 
125 

36 
43 

26 
40 
25 
38 
28 
26 

22 
22 

22 
123 

140 
42 
25 

129 
133 
36 
26 
130 
125 
42 
41 

Mar.  22 
Mar.  17 

May     6 
Jan.    20 

Mar.  22 
...do  

Apr.     2 
Feb.  25 
Feb.  11 

Apr.  11 
Apr.     3 

May  25 
Feb.  17 

Apr.  13 
Apr.     5 

May     2 
Apr.     1 
Mar.  21 
Feb.  17 
Mar.  31 

May  20 
May     8 

May  22 
Apr.  30 
May   14 

May     6 

Mar.  22 
Mar.  23 

Apr.  14 
Apr.  12 

May  18 
June    4 

May  23 
Apr.  29 
May  19 

May  15 
May     6 

May   11 
Apr.  30 

May   12 
May     5 
May     4 
May     5 
May     2 
Apr.  27 

May     2 
May     1 

Mar.  20 
Apr.   13 

May  20 
May     9 
June    3 

May    2 

Apr.  24 
May     9 
May     6 
May     5 
May     8 
Apr.  23 
May     2 

Apr.  26,1910 
Apr.   17,1905 

May   24,1907 
Feb.   14,1908 

Apr.  26,1910 
Apr.     9,  1914 

May   10,1905 
Apr.   15,1913 
Mar.  27,1898 
Mar.   18,1898 
Apr.     9,  1900 

May   15,1896 
2  May     4,  1898 

2  May  29,1902 
2  Apr.  21,1897 
May   17,1895 

May  12,1913 

Mar.  21,1896 
Mar.  13,1914 

Apr.  21,1914 
Apr.  26,1910 

June  16,1895 
July     1,  1900 

May  31,1897 
May     7,1906 
May  31,1897 

May  25,1907 
May   14,1895 

May   12,1895 
May     4,1907 

May  27,1907 
.....do  
Mav   15,1907 
May     9,  1906 
May     4,  1907 
May   15,1907 

May   14,1895 
May   15,1895 

Mar.  23,1914 
Apr.  26,1910 

June     5,  1910 
May   17,1913 
June  11,  1899 

2  May  12,1907 
May   10,1906 
May   12,1907 
May   16,1910 
2  May   12,1907 
2  May  12,1904 
Apr.  21,1897 
2  May  12,1907 

Apr.  26,1910 
Apr.  17,1905 

June  11,1892 
Mar.  15,1881 

Apr.  26,1910 
Apr.     9,  1914 

May   10,1905 
Apr.  28,1894 
Apr.   17,1892 
Mar.  18,1898 
Apr.     9,  1900 

June    6,  1893 
May   23,1893 

2  May  29,1902 
May  30,1884 
2  May  17,1888 

May  12,1913 

Apr.     6,1891 
Mar.  30,1894 

Apr.   21,1914 
Apr.  26,1910 

June  16,1895 
July     1,1900 

May  31,1897 
May   11,1857 
May  31,1897 

May  25,1907 
May   15,1888 

May  31,1889 
May     8,1885 

May   27,1907 
do  

May    15,1907 
May   20,1894 
....do  
May   15,1907 

May   14,1895 
May   15,1895 

Mar.   27,1894 
Apr.  26,1910 

June     5,  1910 
May   17,1913 
2  June  11,  1892 

2  May  12,1907 
May   10,1906 
May   29,1894 
May   16,1910 
2  May   12,1907 
2  May  12,1904 
Apr.  29,1874 
2  May  12,1907 

Uniontown  
Arizona: 
Hoi  brook  

Perry  
Navajo.. 

273 

5,500 
141 

158 
481 

2,650 
851 
71 
130 

84 

5,272 
4,685 

900 
117 
400 

20 

108 
125 

600 
365 

2,739 
1,665 

678 
519 
700 

620 
525 

861 
614 

1,951 
2,513 
1,188 
800 
997 
1,377 

500 
930 

33 

Yuma 

Yuma  

Ouachita... 
Sebastian.. 

El  Dorado.. 
Riverside.. 
Sacramento 
Santa  Barbara 
Yuba  

Denver  

Arkansas: 
Cam  den 

Fort  Smith  

California: 
Georgetown  

Riverside 

Sacramento  

Santa  Barbara 

Wheatland  
Colorado: 
Denver.... 

Feb.  27 

May     4 
Apr.  27 

May     6 
Apr.  17 
May     1 

Apr.  22 

Feb.  11 
Feb.  24 

Apr.     2 
Mar.  20 

Apr.  27 
May  11 

May     5 
Apr.  16 
May     1 

Apr.  27 
Apr.  22 

Apr.  23 
Apr.  15 

Apr.   17 
Apr.  19 
...do  
Apr.  14 
Apr.  10 
...do  

Apr.  18 
Apr.  17 

Feb.  27 
Mar.  24 

May     2 
Apr.  28 
May   18 

Apr.  15 
Apr.  11 
Apr.  21 
Apr.   18 
..do  
Apr.   19 
Apr.     9 
Apr.   17 

Pueblo  

Pueblo  

Connecticut: 
Canton. 

Hartford 

New  Haven. 

New  Haven.  .  . 
do 

Water  bury.. 

Delaware: 
Millsboro... 

Sussex 

Florida: 
Jacksonville.. 

Duval.  .  . 

Pensacola  

Escambia  

Oglethorpe.... 
Worth  

Georgia: 
Point  Peter 

Poulan  

Idaho: 
Boise  
Porthill... 

Ada  
Bonner  

Illinois: 
Aurora  

Kane  

Peoria.... 

Peoria  

Philo.... 

Champaign  — 
Cass.  .  . 

Indiana: 
Logansport  

Vevay  

Switzerland... 
Polk 

Iowa: 
Des  Moines.... 

Keokuk  

Lee  

Kansas: 
Ashland  

Clarke  

Dodge  City  
Horton...     . 

Ford  
Brown 

Independence  

Montgomery.. 
Shawnee 

Tope^a... 

Wichita.... 

Sedgwick  
Warren 

Kentucky: 
Bowfing  Green  
Mount  Sterling  
Louisiana: 
Donaldsonville  
Liberty  Hill. 

Montgomery.. 

Ascension... 
Bienville. 

Maine: 
Cornish  

Eastport 

York  
Washington  .. 
Franklin  

Allegany  
Frederick..  .. 
Harford  
Frederick..  .. 
Montgomery  .  . 
Frederick  

784 
76 
450 

623 
720 
450 
275 
200 
5.50 
112 
392 

Farmington  

Maryland: 
Cumberland 

Emmitsburg  

Fallston  

Frederick     .  .  . 

Great  Falls 

New  Market  

Washington,  D.  C 

Woodstock. 

Baltimore  

1  Broken  record. 


ASTRONOMY,   METEOROLOGY,  AND  SEISMOLOGY. 
records  for  selected  stations. 


11 


First  killing  frost  in  autumn. 

Number  of  consecutive  days  without 
killing  frost. 

Years 
of 
record. 

Average 
date. 

Earliest  date. 

Years 
of 
record. 

Aver- 
age. 

81- 
100 
years. 

Shortest  number 
of  days. 

9-10 

years. 

1895-1914. 

Since  begin- 
ing  of  record. 

1895-1914. 

Since  be- 
ginning of 
record. 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

127 
126 

124 
37 

Nov.    6 
Nov.  10 

Oct.    15 
Dec.  21 

Oct.    24 
Oct.    25 

Sept.  29 
Nov.  25 

Oct.    21,1913 
...    do  

Oct.    21,1913 
do  

126 
25 

124 
37 

229 
238 

152 
335 

196 
205 

127 
281 

186—1910 
203—1904 

139—1908 
284—1908 

186—1910 
203—1904 

136—1894 
276—1893 

Sepfc  22,  1895 
2  Nov.  25,1906 

Sept.  22,  1895 
Nov.  17,1880 

122 
33 

Nov.    3 
Nov.    5 

Oct.    16 
Oct.    23 

Oct.    14,1907 
Oct.    22,1898 

Oct.    14,1907 
Oct.    15,1893 

22 
33 

226 
226 

186 
201 

179—1910 
a  208—1895 

179—1910 
200-1893 

125 
124 
131 
125 
26 

Nov.  16 
Dec.     8 
Nov.  27 

Oct.    24 
Nov.  11 
Nov.    2 
Dec.     8 
Nov.  11 

2  Oct.   15,1897 
Nov.  12,1904 
Nov.  11,1911 
Nov.  28,  1910 
Nov.    4,1895 

Oct.    15,1897 
Nov.  12,1904 
Oct.    17,1893 
Nov.  28,  1910 
Nov.    4,1895 

125 
124 
31 
125 
26 

228 
286 
289 

"278" 

175 
224 
226 
294 
225 

a  167—1899 
233—1913 
241—1898 
298—1910 
240—1908 

2  167—1899 
215—1894 
212—1892 
298—1910 
240—1908 

Dec.     2 

42 
27 

30 
42 

28 

Oct.     6 
Oct.     7 

Oct.     3 
Oct.   21 
Oct.     6 

Sept.  22 
Sept.  26 

Sept.  22 
Oct.     9 
Sept.  22 

Sept.  12,  1902 
do 

Sept.  12,  1902 
do  

42 
26 

30 
42 
28 

156 
163 

150 

187 
158 

125 
141 

123 
162 
131 

134—1912 
139—1902 

125—1905 
a  175—1899 
132—1911 

110—1875 
132—1893 

125—1905 
142—1884 
113—1888 

Sept.  15,  1913 
Oct.     2,  1899 
Sept.  14,1911 

Sept.  15,  1913 
Sept.  30,  1888 
Sept.    7,1888 

22 

Oct.   20 

Oct.     9 

Oct.     2,  1895 

Oct.     2,  1895 

121 

181 

156 

154—1906 

154—1905 

59 
36 

Dec.     6 
Dec.    9 

Nov.  14 
Nov.    8 

Nov.  13,  1906 
Oct.    27,1898 

2  Nov.  12,  1892 
Oct.    27,1898 

59 
35 

297 

288 

237 
230 

262—1914 
247—1898 

230-1894 
227—1894 

125 
25 

Oct.   30 
Nov.    7 

Oct.    15 
Oct.    24 

Oct.    11,1906 
Oct.    21,1913 

Oct.    11,1906 
Oct.    21,1913 

125 

24 

211 
232 

184 
195 

182—1907 
186—1910 

182—1907 
186—1910 

136 
121 

Oct.    14 
Sept.  27 

Sept.  27 
Sept.  14 

Sept.  22,  1895 
Sept.  13,  1907 

Sept.  22,  1895 
Sept.  13,  1907 

133 
121 

170 
139 

132 
102 

98—1895 
89—1900 

98—1895 
89—1900 

127 
59 
22 

Oct.     7 
Oct.    19 
Oct.     3 

Sept.  22 
Oct.     6 
Sept.  16 

Sept.  20,  1896 
Oct.     5,  1901 
Sept.  13,  1902 

Sept.  17,  1890 
Oct.      1,  1856 
Sept.  13,  1902 

126 
59 
22 

155 

188 
155 

122 
160 
120 

126—1895 
152—1906 
113—1897 

126—1895 
152—1906 
113—1897 

123 
27 

Oct.    13 
Oct.   23 

Sept.  27 
Oct.     8 

Sept.  21,  1897 
a  Sept.  30,1895 

a  Sept.  21,  1887 
«  Sept.  30,  1895 

123 
25 

169 
184 

135 
155 

142—1907 
139—1895 

142—1907 
139—1895 

37 
43 

Oct.   10 
Oct.   15 

Sept.  25 
Sept.  29 

Sept.  22,1913 
do  

Sept.  13,  1890 
Sept.  18,1875 

36 
43 

170 
183 

137 
152 

141—1895 
155—1909 

119—1889 
139—1875 

26 
40 
25 
38 
28 
27 

Oct.   20 
Oct.    18 
Oct.    15 
Oct.    22 
Oct.    15 
Oct.    20 

Oct.     5 
...do  
Oct.     1 
Oct.     5 
Oct.     1 
Oct.     4 

Sept.  26,  1912 
Sept.  23,  1895 
Sept.  17,  1901 
Sept.  26,  1912 
Sept.  29,  1899 
Sept.  23,  1895 

Sept.  26,  1912 
Sept.  23,  1895 
Sept.  17,  1901 
Sept.  26,1912 
Sept.  28,  1888 
Sept.  23,  1895 

26 
40 
25 

38 
28 
26 

186 
182 
179 
191 
188 
193 

146 
153 
150 
153 
152 
160 

134—1907 
l<6—  1907 
a  150-1907 
154—1906 
164—1909 
164—1909 

2  134—1894 
149—1891 
a  U  0—1907 
141—1894 
141—1894 
163—1892 

121 
22 

22 
24 

Oct.    18 
Oct.    17 

Nov.  23 
Nov.    4 

Oct.     7 
Oct.     5 

Nov.    3 
Oct.    19 

Sept.  30,  1899 
do  

Sept.  30,  1899 
do  

121 
22 

22 
23 

182 
183 

269 
225 

158 
157 

228 
189 

140-1895 
138—1895 

227—1899 
185—1910 

140—1895 
138—1895 

227—1899 
185—1910 

Oct.    27,1898 
Oct.    14,1907 

Oct.   27,1898 
Oct.    14,1907 

140 
140 
25 

Oct.     2 
Oct.   23 
Sept.  20 

Sept.  20 
Oct.     9 
Sept.    7 

Sept.  10,1913 
Sept.  22,  1904 
Sept.    5,1896 

Sept.  10,1913 
Sept.  22,  1904 
Sept.   5,1896 

MO 
140 
25 

153 
178 
125 

123 
153 
96 

a  110—1910 
150-1904 
97—1899 

a  110—  1910 

150-1904 
89-1892 

129 
135 
36 
26 
131 
125 
43 
41 

Oct.   21 
Oct.   27 
Oct.   20 
Oct.   24 
Oct.    19 
Oct.   22 
...do.... 
Oct.    14 

Oct.     6 
Oct.   14 
Oct.     8 
Oct.     9 
Oct.     6 
Oct.     7 
Oct.     8 
Oct.     2 

Sept.  29,1914 
Oct.     7,1899 
Oct.     3,  1899 
Sept.  23,  1904 
Oct.     1.189.) 
Sept.  22,  1904 
Oct.     2,18.9 
Sept.  23,  1904 

Sept.   6,1892 
2  Oct.     7,  1883 
Oct.     3,1899 
Sept.  23,  1904 
Oct.     1.1899 
Sept.  22,  1904 
Oct.     2.  1899 
Sept.  23,  1904 

129 
133 
36 
26 
130 
125 
42 
41 

189 
199 
182 
189 
184 
186 
196 
180 

157 
173 
152 
156 
154 
152 
168 
153 

163-1913 
154—1906 
154—1906 
a  154—1904 
154—1906 
133—1904 
173—1904 
154—1904 

133-1892 
154-1906 
139—1894 
a  154-1904 
154-1906 
133—1904 
161-1888 
153—1882 

2  And  also  later  years. 


12  PROCEEDINGS  SECOND   PAN   AMERICAN   SCIENTIFIC   CONGRESS. 

TABLE  1. — Summary  of  frost  records 


Station. 

n 
1 

County. 
2 

Alti- 
tude. 

3 

Last  killing  frost  in  spring. 

Year^ 
of 
rec- 
ord. 

4 

Average 
date. 

5 

Latest  date. 

9-10 
years. 

6 

1895-1914. 

7 

Since  be- 
ginning of 
record. 

8 

Massachusetts: 
Blue  Hill  Observ'y 
Concord 

Norfolk.. 

640 
139 
53 
420 
88 
40 
298 
711 

609 
707 
955 
614 
975 

1,039 
863 
935 
1,251 
1,300 

500 
126 

.982 
1,265 
864 
797 

3,041 
2,487 

27 
128 
27 
27 
139 
41 
40 
138 

40 
129 
135 
26 
35 

25 
25 
34 
28 
127 

122 
24 

31 
»27 
25 
36 

132 
33 
35 

128 

128 
139 
43 
26 

128 
27 
136 

26 
27 

139 
22 

23 
140 

135 
25 

130 
40 
27 

40 
125 
132 

126 
30 
27 
26 

Apr.  29 
May     9 
May   13 
May   14 
Apr.   15 
Apr.  20 
May     7 
May     3 

May   14 
Apr.  26 
Apr.  27 
May   15 
Apr.   27 

May   12 
Mav   16 
May   14 
May   16 
May   12 

Mar.  18 
Mar.  19 

Apr.   18 
Apr.   15 
Apr.   18 
Apr.   17 

May  15 
May   16 
May     9 

May   14 

May   13 
Mav     3 
Apr.   16 
May     6 

Mav   21 
May    14 
May   17 

May   22 
May  23 

Apr.  13 
May   11 

Apr.   12 
Apr.  25 

May     4 
May   19 

Apr.     7 
Apr.   17 
Apr.  13 

May   12 
May  13 
May   27 

Apr.  30 
Apr.  19 
Mav     1 
Apr.  17 

May   13 
May   20 
Mav   28 
...d*.  ... 

Mav   21,1906 
May   29,1900 
June    3,  1908 
do  

Mav   21,1906 
Mav   29,1900 
June    3,  1908 
June     8,  1894 
2  May     2,1895 
May   30,  1884 
June.  14,1912 
May   24,1905 

June    9,  1897 
Mav   28,1894 
Mav   24,1910 
Mav   29,1894 
May   26,1897 

Juno     7,  1901 
2  June    7,1897 
June     8,  1885 
June  11,1903 
June     1,  1901 

Apr.   25,1910 
Apr.   26,1910 

May   15,1907 
Mav     9,  1906 
May   16,1890 
May     7,  1906 

«  June  21,1892 
June     6,  1901 
June    9,  1880 

June  26,1892 

June     1,1906 
May   23,1893 
May    19,1894 
June  21,1902 

June  24,1905 
June  11,1894 
June  22,1908 

June  15,1913 
June  10,1913 

Apr.  30,1874 
May   30,1906 

May     8,1896 
May  18,1878 

June     9,  1913 
June  16,1898 

May   10,1906 
Mav   15,1910 
May   11,1906 

June    7,  1901 
June    6,  1910 
June  21,1902 

May   28,1907 
May    12,1913 
May   28,1907 
May   17,1895 

Middlesex  
Plymouth  
Hampden  
Bristol 

Middleboro  

New  Bedford 

Apr.  28 
May     7 
May   24 
May   16 

Mav   28 
May   13 
Mav   14 
May  27 
May   16 

Mav  28 
June     2 
June     1 
June     2 
May   29 

Apr.   10 
Apr.     8 

May     3 
May     1 
May     5 
Apr.  30 

June    2 
May   30 
May   26 

May  30 

May   24 
May  15 
May     1 
May  24 

June  11 
June    5 
June    6 

June    8 
June    6 

Apr.  25 
May   23 

May     3 

May     7 

May  21 
June    4 

Apr.  24 
May     2 
Apr.  30 

May  25 
May  29 
June  14 

May  17 
May     6 
May   19 
May     3 

2  May     2,  1895 
Mav   11,1900 
June  14,1912 
May   24,1905 

June    9,  1897 
Mav   20,1895 
May   24,1910 
May   28,1907 
May  26,1897 

June     7,  1901 
2  June    7,  1897 
do 

Somerset  

...do  

Westboro  
Williamstown  

Worcester  
Berkshire  

Alpena 

Michigan: 
Alpena 

Grand  Rapids  .  . 

Kent  

Kalamazoo  
Sault  Ste.  Marie.... 
Thorn  ville 

Kalamazoo  
Chippewa  
Lapeer 

Minnesota: 
Bird  Island 

Renville 

Crookston  
Moorhead  
Pine  River  Dam... 
Winnibigoshish  
Mississippi: 
Hrookhaven  

Polk  
Clav  
Crow  Wing.... 
Itasca  

June  11,1903 
June    8,  1901 

Apr.  25,1910 
Apr.  26,1910 

May   15,1907 
May     9,  1906 
....'.do  

May     7,  1906 

June  21,1902 
June     6,  1901 
June     3,  1910 

June     6,  1909 

'June     1,  1906 
May   16,  1912 
'  Mav     1,  1903 
June  21,1902 

June  24,1905 
June     7,  1906 
June  22,1908 

June  15,1913 
June  10,1913 

2  Apr.  21,1907 
May  30,1906 

May     8,  1896 
May   15,1907 

June     9,  1913 
June  16,1898 

May   10,1906 
May   15,1910 
May  11,1906 

June    7,  1901 
June    6,  1910 
June  21,1902 

May   28,1907 
May   12,1913 
May   28,1907 
May    17,1895 

Lincoln  

Greenville  . 

Washington... 

Nodaway  
Laclede 

Missouri: 
Conception  

Lebanon  . 

Liberty 

Clay 

Mexico  

Audrain 

Montana: 
Crow  Agencv  
Havre  '  

Bighorn.  .  . 
Hill  

Helena 

Lewis       and 
Clark. 
Sheridan  

do 

4,110 
2,020 

3,821 
2  821 

Poplar 

Nebraska: 
Hav  Springs 

North  Platte  

Lincoln 

Omaha  

Douglas 

1  103 

Valentine 

Cherry 

2,598 

4,720 
4,500 
4,291 

126 
500 

16 
719 

3,863 
7,013 

928 
1,038 

500 
1,186 
81 

1,674 
1,944 
789 

960 
627 
1,050 

527 

Nevada: 
Carson  City 

Ormsby 

Reno 

Washoe 

Wjnnemucca. 

Humboldt  

Rockingham.. 
Grafton 

New  Hampshire: 
Newton 

Plvmouth. 

New  Jersey: 
Atlantic  City  
Charlotteburg 

Atlantic  
Passaic 

New  Mexico: 
Agricultural  College 
Santa  Fe  

Dona  Ana  
Santa  Fe  

Tompkins.  .  . 
SchuyJer 

New  York: 
It'iaca 

PerrvCity.  ... 

North  Carolina: 
Chapel  Hill  

Orange 

Lenoir  

Caldwell 

Weldon  

Halifax 

North  Dakota: 
Bismarck 

Burleigh... 
Williams  
Pembina  

Licking 

Buford  

Pembina.  . 

Ohio: 
Gran  ville  

Marietta  

Washington... 
Jefferson  
Scioto  

New    Alexandria.. 
Portsmouth  

Broken  record. 


ASTRONOMY,   METEOROLOGY,   AND   SEISMOLOGY, 
/or  selected  stations — Continued. 


First  killing  frost  in  autumn.                 » 

Number  of  consecutive  days  without 
killing  frost. 

Earliest  date. 

Shortest  number 
of  days. 

Years 
of 

Average 

Years 
of 

Aver- 

81- 
100 

record. 

date. 

9-10 

years. 

1895-1914. 

Since  begin- 
ning ol  record 

record 

age. 

years 

1895-1914. 

Since  be- 
ginning of 
record. 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

27 

Oct.   12 

Sept.  29 

Sept.  22  1904 

Sept.  17,  1893 

27 

166 

139 

142—1904 

142—1904 

129 

Oct.     2 

Sept.  15 

Sept.  11,1914 

Sept.    2,1886 

128 

146 

118 

119—1895 

1  19—1895 

27 

Sept.  29 

Sept.  19 

Sept.  14.1011 

Sept.  14,1911 

27 

139 

114 

114—1900 

114—1900 

126 

Sept.  23 

Sept.    9 

Sept.    6,1902     Sept.    fi,  1902 

126 

132 

104 

105-1908 

105—1008 

139 

Oct.    27 

Oct.    12 

Sept.  22.  1904 

Sept.  22.  1904 

139 

195 

167 

152—1904 

1  .-,2—  1904 

41 

<>t.    16 

Oct.     4 

Sept.  23.1904 

Sept.  23,  1904 

41 

179 

150 

153—1904 

133—1884 

40 

O-t.     3 

Sept.  15 

Sept.  14,1911 

Sept.    4,1883 

40 

143 

114 

107—1912 

107—1912 

»40 

Oct.     9 

Sept.  26 

..      do 

Sept.  14,1911 

i  38 

158 

133 

123  1913 

123  1913 

40 

Sept.  29 

Sept.  13 

Sept.  10,  1898 

Sept.    6.18S5 

40 

138 

111 

104—1897 

98—1894 

31 

Oct.    13 

Sept.  23 

Sept.  14.1899 

Sept.    6,1892 

129 

170 

133 

129-1902 

129—1902 

»34 

Oct.    21 

Oct.     2 

Sept.  22.1904 

Sept.  22,1904 

134 

177 

141 

127—1907 

127—1907 

27 

Sept.  27 

Sept.  14 

Sept.  14,1913 

2  Sept.    5,1888 

26 

135 

110 

112—1913 

102—1891 

35 

Oct.    11 

Sept.  24 

do  

Sept.  14,1913 

35 

167 

131 

118—1897 

118-1897 

25 

Sept.  28 

Sept.  11 

2  Sept.   9,1898 

«Sept.    9.1898 

25 

139 

106 

96-1910 

96—1910 

25 
34 

Sept.  23 
...do  

Sept.    7 
Sept.    5 

do 

Aug.  28.1893 
Aug.  25.1885 

25 
34 

130. 
132 

97 

96 

*  102—1897 
102—1897 

92—1893 

78—18S5 

Sept.    8  1S98 

28 

Sept.  17 

Sept.    4 

Aug.  29.1911 

Aug.  29.1911 

28 

124 

94 

83—1905 

83-1905 

28 

Sept.  27 

Sept.  15 

Sept.  10,1898 

Sept.  10,1898 

127 

138 

109 

104—1901 

104—1901 

123 

Nov.    5 

Oct.   22 

2  Oct.   22.1895 

Oct.   20.1811 

122 

232 

195 

187—1910 

187—1910 

24 

Nov.    8 

Oct.    25 

Oct.    21,1895 

Oct.    21,18  5 

24 

234 

200 

186—1910 

186—1910 

130 

Oct.    19 

Oct.     5 

Sept.  28.1908 

Sept.  28.  190S 

130 

184 

155 

148—1908 

148—1908 

127 
25 

Oct.    21 
Oct.    10 

Oct.     9 
Sept.  23 

Sept.  30.  1S95 
Sept.  13,  1902 

Sept.  30,  1895 
"Sept.  13.1890 

127 
25 

189 

175 

Ifil 
141 

153—1906 
*  148—1902 

153—1906 
119—1890 

36 

Oct.    17 

Sept.  30 

do  

Sept.  13,  1902 

36 

183 

153 

*  149—1902 

»  149-1902 

13« 

Sept.  25 

Sept.    5 

Aug.  27,1908 

Aug.  27,1908 

132 

133 

95 

82—1902 

82—1902 

33 

Sept.  18 

Sept.    3 

Aug.  25.1910 

Aug.  25,1910 

33 

125 

96 

83—1910 

83-1910 

35 

Sept.  26 

Sept.    7 

do  

do  

35 

140 

104 

83-1910 

83—1910 

129 

Sept.  13 

Aug.  30 

Aug.  22,1908 

Aug.  22,1908 

128 

122 

92 

»  92—1908 

71-1892 

128 

Sept.  19 

Sept.    6 

Aug.  25.1910 

Aug.  25.1910 

128 

129 

105 

95—1910 

95—1910 

141 

Sept.  29 

Sept.  15 

Sept.  12.  1902   J  Sept.  10.  1876 

139 

149 

123 

134—1805 

118—1893 

43 

Oct.    12 

Sept.  24 

Sept.  18.  1901     Sept.  18.1901 

43 

179 

146 

153—1901 

140—1890 

26 

Sept.  30 

Sept.  15 

Sept.  12,  1902     Sept.  12,  1902 

26 

147 

114 

83—1902 

83-1902 

128 

Sept.  21 

Sept.    3 

Sept.    2.1898 

Sept.    2,1898 

128 

123 

84 

82—1897 

82—1897 

28 

Oct.     3 

Sept.  17 

Sept.  -6  1900 

Sept.    6.1900 

27 

142 

104 

108—  18931 

93—1894 

136 

Sept.  24 

Sept.    7 

Aug.  22.1899 

Aug.  22,1899 

136 

130 

93 

93-1908 

92—1894 

26 

Sept.  23 

Sept.    8 

Aug.  29.1908 

Aue.  29.1908 

26 

124 

02 

*  87—1908 

2  87—1908 

126 

Sept.  24 

Sept.  13 

Sept.  10,  1913 

Sept.    7,1888 

126 

124 

99 

92-1913 

92—1913 

MO 

Oct.    30 

Oct.    19 

Oct.      1.1899 

Oct.      1,1899 

139 

200 

177 

173—1899 

161—1888 

22 

Sept.  26 

Sept.  15 

Sept.  14,1911 

Sept.  14,  1911 

22 

138 

115 

108-1902 

108—1902 

23 

Oct.    22 

Oct.    11 

Oct.    10.1909 

Oct.      1,1894 

23 

193 

161 

163—1899 

155—1894 

MO 

Oct.    19 

Oct.     6 

Sept.  27,  1908 

Sept.  25,  1889 

140 

177 

152 

146—1908 

143—1880 

136 

Oct.    10 

Sept.  27 

Sept.  14.  1911 

Sept.  14.1911 

135 

159 

129 

116—1895 

116—1895 

25 

Sept.  26 

Sept.  10 

Sept.    5.1906 

Sept.    5.1906 

25 

130 

98 

84-1906 

84—1906 

130 

Oct.    28 

Oct.    13 

2  Oct.      1,1895 

Oct.     1,  1895 

130 

204 

172 

153—1906 

153—1906. 

»36 

Oct.    18 

Oct.     4 

.....do  

Sept.  30,  1888 

i  36 

184 

155 

153—1906 

153  —  iQ06 

26 

Oct.    24 

Oct.    12 

Oct.    10,1895 

Oct.     9,  1889 

26 

194 

165 

152—1906 

152—1906 

40 
»28 

Sept.  19 
Sept.  23 

Sept.    5 
Sept.    9 

Aug.  31,1895 
Sept.    9,  1910 

Aug.  23,1891 
Sept.    5,  1881 

40 
125 

130 
133 

103 
103 

102—1895 
95—1910 

98—1888 
95—1910. 

132 

Sept.  12 

Aug.  27 

Sept.    8,1901 

Aug.  20,1875 

132 

108 

74 

83—1902 

2  70—1875 

125 

Oct.     8 

Sept.  22 

Sept.  15,  1902 

S*ept.  15,1902 

125 

161 

128 

130—1895 

130—1895 

31 

Oct.    21 

Oct.     8 

Oct.      1,  1895 

2  Oct.     1,  1895 

30 

185 

155 

153—1906 

148—1886. 

27 

Oct.    11 

Sept.  28 

Sept.  30,  1908 

Sept.  26,  1X87 

26 

163 

132 

125—1907 

125—1907 

26 

Oct.    21 

Oct.      4 

Oct.     1,  .1  <95 

»  Oct.     1,  1895 

26 

187 

154 

136—1895 

136—1895, 

And  also  later  yaars. 


14  PROCEEDINGS  SECOND  PAN  AMERICAN   SCIENTIFIC   CONGRESS. 

TABLE  1. — Summary  of  frost  records 


Station. 

1 

County. 
2 

Alti- 
tude. 

3 

•                   Last  killing  frost  in  spring. 

Years 
of 
rec- 
ord. 

4 

Average 
date. 

5 

Latest  date. 

9-10 

years. 

6 

1895-1914. 

7 

Since  be- 
ginning of 
record. 

8 

Oklahoma: 
Healdton 

Carter 

900 
1,247 

1,940 
266 
1,640 
510 
112 

1,327 
455 

250 
160 

51 
711 

1,352 
1,636 
1,306 
1,788 
3,231 
3,647 

1,028 
347 

1,738 
1,050 

720 

4,000 
4,360 

876 
700 

40 
1,450 
681 
2,135 
13 
60 
1,380 

45 
1,943 
1,000 

1,933 
435 

586 
681 
974 
616 

6,088 
7,188 

21 
24 

25 
25 
26 
37 
39 

31 
31 

25 
30 

22 
21 

224 
26 
33 
27 
27 
«25 

44 

43 

29 

231 

25 

25 
40 

28 
234 

28 
246 
240 
29 
42 
226 
25 

37 
33 
29 

23 
23 

28 
42 
235 
31 

42 
24 

Apr.     5 
Apr.     2 

Apr.  17 
Apr.  24 
Apr.  18 
Apr.   15 
Apr.  14 

May  17 
Apr.  16 

Apr.  29 
Apr.  22 

Mar.  26 
Mar.  25 

Mav   14 
May  19 
May   12 
May     6 
..do  
May     8 

Apr.    3 

Mar.  22 

...do  
Feb.  27 

Mar.    4 

Apr.  20 
Apr.  21 

May  16 
May  14 

Mar.  30 
Apr.  28 
Apr.     9 
Apr.  23 
Mar.  25 
Apr.  10 
Apr.  19 

Apr.  22 
Apr.  12 
Mar.  30 

Apr.  25 
Apr.  19 

May     6 
Apr.  27 
Apr.  23 
May     2 

May  21 
May  31 

Apr.  25 
Apr.  22 

May   12 
...do  
May     4 
May   10 
Apr.  30 

June    9 
Apr.  28 

May   10 

May     4 

Apr.  13 
Apr.  10 

May  30 
June    5 
May   29 
May   19 
May   18 
May  28 

Apr.  17 
Apr.  10 

Apr.     9 
Mar.  23 

Mar.  20 

May     6 
May  14 

June    6 
June    4 

Apr.  14 
May   14 
Apr.  25 
May     8 
Apr.  12 
Apr.  27 
May     2 

May  17 
May     9 
Apr.  20 

May  10 
May     4 

May  21 
Mav  15 
May     6 
May  20 

June    3 
June  20 

'May     1,1903 
'Apr.  30,1903 

May   18,1901 
May   10,1908 
do 

i  May     1,  1903 
!Apr.  30,1903 

May   18,1901 
May    18,1892 
May  10,1908 
May   24,1881 
May    12,1887 

June  14,1912 
May   12,1892 

May   12,1907 
do 

Oklahoma  City  
Oregon: 
Ashland  

Oklahoma  
Jackson  

Corvallis 

Benton  ... 

Jackson 

Roseburg 

Douglas 

do....... 
May     1,  1905 

June  14,1912 
May     2,  1903 

May   12,1907 
.do  

The  Dalles 

Wasco  

Pennsylvania: 
Wellsboro  
West  Chester.  . 

Tioga  
Chester  

Rhode  Island: 
Kingston  .. 

Washington... 
Providence  — 

Berkeley 

Providence 

South  Carolina: 
Fergusonand  Trial  3 
Little  Mountain  
South  Dakota: 
Alexandria  

Apr.  17,1905 
do..  

June  21,1902 
June  22,1902 
June  21,1902 
May   30,1897 
May   21,1908 
June  21,1902 

Apr.  23,1904 
Apr.  25,1910 

Apr.  23,1907 
Mar.  26,1913 

Mar.  27,1913 

May  17,1910 
June  18,1895 

June  12,1906 
June  14,1912 

Apr.  21,1897 
May  17,1895 
Apr.  22,1904 
May  15,1910 
Apr.  21,1897 
May  10,1906 
May  15,1910 

May   31,1908 
May     7,  1898 
Apr.  28,1907 

May  16,1910 
do  

May   21,1895 
May   24,1910 
May   11,1907 
iMay  21,1895 

June    1,1903 
July     7,  1904 

Apr.  17,1905 
do  

June  21,1902 
June  22,1902 
June  21,1902 
May   30,1897 
May   21,1908 
June  21,1902 

Apr.  24,1893 
Apr.  25,1910 

Apr.  23,1907 
Apr.  16,1870 

iMar.  27,1894 

May  17,1910 
June  18,1895 

June  12,1906 
June  14,1912 

Apr.  21,1897 
May   26,1886 
May     7,  1891 
iMay   15,1888 
Apr.  26,1888 
May   10,1906 
May  15,1910 

May   31,1908 
June    8,  1891 
Apr.  28,1907 

Mav   16,1910 
do  

May  30,1894 
May   24,1910 
May  13,1888 
May   26,1891 

June  11,1889 
July     7,  1904 

Newberry  
Hanson  

Brookin^s 

Brookings  
Beadle  

Huron  

Kimball  

Rapid  City...  . 

Brule  
Pennington  .  .  . 
Lawrence  

Knox  
Shelby  

Spearfish 

Tennessee: 
Knoxville  
Memphis  

Texas: 
Abilene 

Taylor 

Fort  Clark  (Brock- 
etville). 
New  Braunfels  
Utah: 
Moab  

Kinnev.  . 

Comal...  . 

Grand  

Salt  Lake  City  
Vermont: 
Northfleld  

Salt  Lake  

Washington... 
Windsor 

Woodstock 

Virginia: 
Birdsnest  . 

Northampton. 
Rockingham  .  . 
Campbell 

Dale  Enterprise  
Lynchburg.  .  . 

Marion 

Smvthe 

Norfolk  

Norfolk 

Petersburg  

Dinwiddie.... 
Augusta... 

Staunton...  . 

Washington: 
Olvmpia 

Thurston 

Spokane  

Spokane 

Walla  Walla 

Walla  Walla.. 

McDowell  
Berkeley 

West  Virginia: 
Elkhorn  

Martinsburg 

Wisconsin: 
Green  Bay  . 

Brown 

La  Crosse  

La  Crosse  
Dane  
Manitowoc  

Laramie 

Madison  

Manitowoc 

Wyoming: 
Che  venue..  .  . 

Laramie 

Albany 

i  And  also  later  years. 


2  Broken  record. 


ASTRONOMY,  METEOROLOGY,  AND  SEISMOLOGY. 
for  selected  stations — Continued. 


15 


First  killing  frost  in  autumn. 

Number  of  consecutive  days  without 
killing  frost. 

Years 
of 
record. 

Average 
date. 

Earliest  date. 

Years 
of 
record. 

Aver- 
age. 

81- 
100 

years. 

Shortest  number 
of  days. 

9-10 

years. 

1895-1914. 

Since  begin- 
ning of  record. 

1895-1914. 

Since  be- 
ginning of 
record. 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

21 
24 

Oct.    29 
Nov.    1 

Oct.    18 
Oct.    17 

Oct.    10,1908 
Oct.    20,1905 

Oct.    10,1908 
Oct.     7,  1891 

21 
24 

207 
213 

176 

178 

163—1908 
196—1907 

163—1908 
183—1892 

26 
25 
26 
37 

238 

Oct.    21 
Oct.    16 
Oct.    29 
Nov.  12 
Oct.    23 

Sept.  28 
Sept.  25 
Oct.     7 
Oct.    17 
Oct.      7 

Sept.  13.  1896 
Sept.  21,  1895 
do  

Sept.  13,  1896 
Sept.  21,  1895 
do  

225 
25 
26 
37 
238 

187 
175 
194 
211 
192 

139 
136 
156 
160 
160 

126—1896 
135—1895 
138—1908 
137—1908 
170—1905 

126—1896 
135—1895 
138—1908 
137—1908 
164—1883 

Sept.  24,  1908 
Sept.  25,  1908 

Sept.  24,  1908 
Sept.  25,1908 

32 
31 

Sept.  25 
Oct.    23 

Sept.  11 
Oct.   10 

Sept.    6,1909 
Oct.     3,  1899 

Aug.  25,1884 
Oct.     3,  1899 

31 
31 

131 
190 

94 
165 

92—1913 
171—1906 

92—1913 

168—1888 

25 
229 

Oct.    13 
Oct.    18 

Sept.  27 
Sept.  29 

Sept.  14,  1911 
Sept.  23,  1904 

Sept.  14,  1911 
Sept.  23,  1904 

25 
229 

167 
179 

140 
148 

133—1911 
151—1907 

133—1911 
150—1888 

»21 
22 

Nov.    5 
Nov.  11 

Oct.    22 
Oct.    27 

Oct.    19,1901 
Oct.    25,1903 

Oct.    19,1901 
Oct.    25,1903 

221 

21 

224 
231 

192 
200 

197—1907 
197—1907 

197—1907 
197—1907 

225 
27 
34 
27 
226 
225 

Sept.  26 
Sept.  22 
Sept.  21 
Oct.     1 
Sept.  27 
Sept.  28 

Sept.    8 
Sept.    5 
...do  
Sept.  18 
Sept.  14 
Sept.  13 

Sept.  12,  1902 
Sept.    3,1896 
Sept.  10,  1898 
Sept.  12,  1902 
Sept.  13,  1902 
Sept.  11,  1898 

Aug.  23,1891 
do  

224 
26 
33 
27 
226 
225 

135 
126 
132 
148 
144 
143 

101 
92 
99 
122 
119 
108 

83—1902 
82—1902 
83—1902 
128—1901 
123—1904 
83—1902 

83—1902 
82—1902 
83—1902 
127—1890 
123—1904 
83—1902 

do  

Sept.  12,  1902 
i  Sept.  13,  1890 
Sept.  11,  1898 

44 
43 

Oct.    27 
Nov.    1 

Oct.    10 
Oct.    16 

Oct.      1,  1895 
Oct.    11,1895 

Oct.      1,  1895 
Oct.     2,  1876 

44 
43 

207 
224 

176 

189 

180—1895 
187—1910 

i  180—1876 
184—1893 

29 
225 

Nov.  10 
Nov.  25 

Oct.    25 
Nov.    7 

Oct.    22,1911 
i  Nov.    2,1899 

Oct.    22,1911 
i  Nov.    2,  1899 

29 

225 

233 
271 

199 
229 

209—1899 
244—1906 

209—1899 
239—1876 

26 

...do  

Nov.    9 

Nov.    3,1899 

Nov.    3,1899 

25 

266 

234 

240—1897 

238—1894 

25 
40 

Oct.     5 
Oct.    19 

Sept.  17 
Oct.     2 

Sept.  12,  1898 
Sept.  22,  1895 

Sept.    8,1890 
Sept.  22,  1895 

25 
40 

168 
181 

134 
141 

143—1912 
96—1895 

143—1912 
96—1895 

28 
232 

Sept.  19 
Sept.  27 

Sept.   3 
Sept.  12 

Aug.  31,1909 
Sept.  10,  1913 

Aug.  27,1894 
Sept.    4,1883 

28 
232 

126 
136 

89 
100 

97—1909 
92—1913 

97—1909 
92—1913 

226 
2  46 
42 
29 
42 
«28 
25 

Nov.  18 
Oct.     9 
Oct.    27 
Oct.    11 
Nov.  16 
Oct.    25 
Oct.    15 

Nov.    6 
Sept.  23 
Oct.   11 
Sept.  26 
Nov.    1 
Oct.     9 
Oct.     2 

Nov.  11,1901 
Sept.  22,  1897 
Oct.     2,  1899 
Sept.  16,  1902 
Oct.    28,1903 
Oct.      1,  1895 
i  do  

Nov.    1,  1893 
Sept.  15,  1873 
Oct.     2,  1899 
Sept.  16,  1902 
Oct.    15,1876 
Oct.      1,  1895 
i  do  

226 
«46 
240 
29 
42 
226 
25 

233 

164 
201 
165 
236 
198 
179 

206 
132 
169 
141 
203 
165 
153 

207—1897 
134—1907 
175—1899 
148—1903 
205—1903 
154—1906 
165—1895 

202—1875 
128—1886 
162—1888 
138—1888 
204—1879 
154—1906 
165—1895 

37 
33 
29 

Oct.    28 
Oct.    12 
Nov.    7 

Sept.  28 
Sept.  20 
Oct.   18 

Sept.  21,  1895 
Sept.  10,  1895 
Oct.    19,1905 

Sept.  11,1889 
Sept.  10,  18P5 
Sept.  28,  1886 

37 
33 
29 

189 
183 
222 

134 
134 
181 

114—1908 
142—1895 
191—1905 

114—1908 
115—1891 
176—1886 

23 
24 

Oct.    12 
Oct.    17 

Sept.  27 
Oct.     4 

Sept.  14,  1902 
Sept.  23,  1913 

Sept.  14,  1902 
Sept.  23,  1913 

23 
23 

170 
181 

140 
153 

134—1913 
134—1913 

134—1913 
134—1913 

28 
42 
37 
31 

Oct.     9 
Oct.    11 
Oct.   18 
Oct.   13 

Sept.  23 
Sept.  29 
Oct.     3 
Sept.  29 

Sept.  23,  1899 
Sept.  29,1908 
do  

Sept.  16,  1887 
Sept.  21,1889 
Sept.  29,  1908 
Sept.  27,  1912 

28 
42 
235 
31 

156 
167 
178 
164 

125 
137 
160 
132 

131—1895 
147_1895 
150—1908 
141—1895 

116—1894 
122—1889 
150—1908 
133—1891 

Sept.  27,  1912 

42 
24 

Sept.  17 
Sept.  10 

Aug.  31 
Aug.  29 

Aug.  25,1910 
Aug   22,1904 

Aug.  25,1900 
Aug.  16,  1  893 

42 
24 

119 
102 

89 
70 

94—1910 
45—1904 

85—1889 
45—1904 

8  Trial,  elevation  85  feet,  1893-1910  (18  years);  Ferguson,  elevation  51  feet,  1911-1914  (4  years). 


16 


PROCEEDINGS   SECOND   PAN   AMERICAN    SCIENTIFIC    CONGRESS. 


In  the  determination  of  these  averages  a  number  of  interesting  mathematical 
and  meteorological  problems  arose,  all  of  which  required  working  solutions, 
although  the  correct  solution  has  not  yet  necessarily  been  found.  For  example, 
when  the  average  dates  were  determined  there  wras  usually  a  fraction  of  a  date 
to  be  disposed  of.  The  date  is  a  discrete  thing,  not  subject  to  division,  hence 
the  whole  fraction  must  be  thrown  in  one  direction  or  the  other.  At  first  the 
fraction  was  disposed  of  according  to  the  usual  rule;  that  is,  when  less  than 
0.5  the  fraction  was  dropped,  and  when  more  than  0.5  the  date  was  increased  by 
a  whole  day.  Later  the  average  dates  were  checked  by  charting  for  the  spring 
the  date  of  last  killing  frost  for  a  number  of  stations  (see  fig.  2).  The  dates 


STATIONS 

DAYS   BEFORE  AVERAGE    AVERAGE      DAYS  AFTER   AVERAGE 

40           30           20            10      DATE          IO            2O            3O            4O 

DALE  ENTERPRISE.  VA 
GRAND  RAPIDS.  MICH. 
BISMARCK.  N.DAK. 
ROSALIA.  WASH. 
MEMPHIS.  TENN. 

....::.  : 

.11:. 

.:.::.  : 

:..: 

. 

.  . 

.     :  . 

h::  .. 

H::    . 

:    . 

\ 

. 

..  : 

• 

• 

..     : 

.. 

FIG.  2.— Occurrences  of  last  killing  frost  in  spring  with  reference  to  the 
average  date  at  selected  stations. 

before  and  after  the  average  for  the  whole  period  of  years  were  then  counted 
and  the  exact  meaning  of  a  fraction  of  a  date  in  this  connection  was  carefully 
considered.  The  same  procedure  was  followed  for  the  dates  of  first  killing 
frost  in  fall  (see  fig.  3).  After  a  careful  consideration  the  conclusion  was 
reached  that  a  more  nearly  correct  method  of  disposing  of  the  fractions  of  dates 
in  the  case  of  killing  frost  averages  consists  of  increasing  the  average  date 
of  the  last  killing  frost  in  spring  by  one  day,  whenever  there  is  a  fraction, 
no  matter  how  small,  and  dropping  all  fractions  of  dates  for  the  average  date 
of  first  killing  frost  in  fall,  no  matter  how  much  the  fraction  may  be.  This 
practice  also  has  the  advantage  that  if  there  is  an  error  it  is  on  the  side  of 
safety,  although  here  a  matter  of  a  day  is  not  of  importance. 

The  method  of  determining  the  average  length  of  the  season  without  killing 
frost  has  been  to  count  the  time  between  the  average  date  of  last  killing  frost  in 


STATIONS 

DAYS  BEFORE  AVERAGE   AVERAGE     DAYS  AFTER   AVERAGE. 
40         30          20           10       DATE        |O          20          3O          4O 

DALE  ENTERPRISE.  VA. 
GRAND  RAPIDS.  MICH. 
BISMARCK.  N.DAK. 
ROSALIA.  WASH. 
MEMPHIS.  TENN. 

. 

:.:  : 

:     . 

£••  •  •• 

: 

.:  .  . 

. 

•  • 

. 

: 

:  :..: 

::... 

:.:!.::.* 

« 

.. 

- 

.:  .  . 

- 

. 

.  . 

.:  .  i.:. 

: 

"..     .. 

: 

.  . 

FIG.  3.— Occurrences  of  first  killing  frost  in  fall  with  reference  to  the  average 
date  at  selected  stations. 

spring  and  the  average  date  of  first  killing  frost  in  fall.  This  method  has  the 
advantage  of  avoiding  questions  of  fractions  of  days  and  also  permits  the  use 
of  the  whole  available  record  for  spring  and  for  fall  in  those  cases  where  one 
or  both  are  incomplete. 

Although  the  "average  dates  of  last  killing  frost  in  spring"  and  of  "first 
killing  frost  in  fall"  and  the  "average  length  of  the  season  without  killing 
frost"  are  terms  which  have  been  widely  used,  there  is  still  considerable  doubt 
as  to  the  significance  of  these  terms  and  of  the  figures  representing  them. 
The  average  date  of  last  killing  frost  in  spring  is  that  date  after  which  n 


ASTRONOMY,   METEOROLOGY,  AND   SEISMOLOGY. 


17 


o 

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killing  frost  will  occur  in  approximately  half  the  years.  On  the  average  date 
there  is  an  even  chance  that  the  last  killing  frost  has  occurred.  In  other 
words,  one  crop  out  of  every 
two  will  be  destroyed  by  frost 
if  it  is  susceptible  to  frost  in- 
jury on  the  average  date.  This 
is  a  higher  proportion  than 
even  the  most  productive  agri- 
culture can  stand,  and  con- 
sequently the  average  date 
of  last  killing  frost  has  little 
significance  for  the  farmer; 
this  also  applies  to  the  average 
date  of  first  killing  frost  in 
fall  Some  date  earlier  than 
the  average  date  of  first  kill- 
ing frost  is  the  date  before 
which  the  crop  must  be  har- 
vested or  there  will  be  loss 
from  frost  damage  in  too  many 
years.  There  are  similar  con- 
siderations to  be  met  with  in 
the  average  length  of  the  sea- 
son without  killing  frost.  To 
take  advantage  of  the  whole 
of  this  season  it  is  necessary 
for  it  to  begin  on  the  day  of 
the  last  killing  frost  in  spring 
and  to  continue  until  the  date 
of  the  first  killing  frost  in  fall. 
If  crops  are  planted  so  that 
they  become  susceptible  to 
frost  damage  on  the  average 
date  of  last  killing  frost  in 
spring,  the  crop  in  half  the 
years  will  be  destroyed  in  the 
spring.  This  leaves  only  one 
crop  out  of  two  to  continue 
until  fall.  Then,  if  the  fall 
frosts  occur  at  random  with 
reference  to  the  spring  frost — 
that  is,  if  there  is  no  casual 
relation  between  them  —  one 
crop  out  of  every  two  carried 
through  the  summer  will  be 
destroyed  by  a  killing  frost 
in  fall  before  it  can  be  har- 
vested. These  relations  may 
perhaps  be  shown  to  better 
advantage  by  figure  4.  which 
shows  by  bars  the  total  length 

of    the    growing    season     for     the    following    stations     selected     from     the 
whole    United    States:    Dale    Enterprise,    Va.;    Memphis,    Tenn. ;    and    Bis- 
25807C-2— 17 2 


Lu 


Z2 


iiiiiiiiiiiniiiii  ii  niiiiiiniiiiiitiiM 
iniiiiiiiiiniiii  iiiiiiiiiiiiMiiiiiiiiii 

IIIIIIIMIIIIIIIII   IIIIIIIMIIIIIIIMIIIIII 
IIIIIIUIIIIIUIIIIIIIIIIIIIIIIIIIIIIHIIK 


UJ 


oo^oo    — 

OOOOO>O)O) 


18          PROCEEDINGS  SECOND  PAN  AMERICAN   SCIENTIFIC   CONGRESS. 

ruarck,  N.  Dak.  If  it  were  possible  to  determine  the  latest  date  of 
last  killing  frost  in  spring  for  a  period  covering  a  hundred  years  or  more 
and  the  earliest  date  of  first  killing  frost  in  fall  for  a  similar  period,  we 
should  probably  have  the  season  of  safe  plant  growth.  The  nearest  approach 
possible  to  this  available  is  the  latest  date  in  spring  and  the  earliest  date 
in  fall  which  has  been  observed  since  the  beginning  of  the  record.  In  very 
few  cases  this  is  more  than  40  years,  and  in  most  cases  is  a  great  deal 
shorter  than  this.  These  extreme  dates  of  killing  frosts  represent  different 
things  at  different  places  because  of  the  varying  length  of  the  records.  The 
longer  the  record  the  more  probable  it  is  that  these  extreme  dates  will  not 
be  exceeded,  but  as  extreme  dates  rest  on  single  occurrences,  they  can  not 
be  considered  as  absolute  limits.  The  shortest  recorded  season  without  killing 
frost  is  usually  somewhat  longer  than  the  period  between  the  latest  date  of  last 
killing  frost  in  spring  and  the  earliest  date  of  first  killing  frost  in  fall,  because 
in  most  cases  these  extreme  dates  did  not  occur  in  the  same  year. 

THE    PROBABILITY    OF    FBOST. 

. 

The  date  of  the  last  killing  frost  in  1  year  in  20  established  the  extreme 
limit  for  killing  frost  in  spring  in  that  20-year  period;  in  each  of  the  other 
19  years  the  date  of  the  last  killing  frost  is  earlier  than  that.  If  the  20-year 

period  has  the  exact  average 
frost  distribution  the  prob- 
able occurrence  of  the  last 
killing  frost  in  1  year  in  20 


can    be    predicted    on    that 

o    .    . 


FIG.  5.—  Frequency  polygon  and  most  probable  normal  fre-  Under     similar     average 

quency  curve  of  the  date  of  last  killing  frost  in  spring  for  conditions  the  latest  date 
the  combined  records  61  33  stations,  comprising  823  obser-  Qf  lagt  kming  frogt  during 
vations. 

any   10  years   will   give  the 

date  on  or  after  which  frost  may  be  expected  once  in  10  years.  How- 
ever, it  is  hardly  possible  that  any  given  20  or  10  year  period  will  give 
the  .  exact  average  frost  distribution,  especially  in  the  cases  which  occur 
but  once  or  twice  during  the  period.  It  is  desirable  to  determine  as  far 
as  possible  the  risk  from  frost  damage  after  any  particular  date.  This 
has  been  attempted  by  various  methods,  the  most  notable  of  which  is  perhaps 
the  table  prepared  by  Wilson1  for  New  York  State.  This  method,  however, 
has  the  disadvantage  that  the  curve  of  frost  occurrence  used  by  him  is  not 
smooth,  which  results  from  the  fact  that  all  the  records  are  too  short.  To 
obtain  a  smooth  curve  of  the  distribution  of  last  killing  frost  in  spring  in  the 
neighborhood  of  1,000  observations  are  required.  However,  by  grouping  a 
great  many  cases,  it  is  possible  to  determine  the  type  of  distribution  of  these 
recorded  dates  of  last  killing  frost  in  spring.  Table  I  shows  for  a  few  stations 
the  dates  on  or  after  which  the  last  killing  frost  may  be  expected  to  occur  in 
1  year  in  10,  provided  the  period  from  which  the  date  was  calculated  was 
one  with  average  frost  conditions. 

Figure  5  is  a  frequency  polygon  which  has  been  constructed  for  823  observa- 
tions, representing  the  combined  records  of  33  stations  for  last  killing  frost  in 
spring.  An  attempt  was  made  to  fit  this  frequency  polygon  to  various  curves 
of  distribution,  both  normal  and  skew  curves,  by  the  use  of  methods  suggested 

i  Wilson,  Wilford  M.  :  Frosts  In  New  York,  N.  T.  Cornell  Agr.  Fjxp.  Sta.  bul.  316  :  536- 
543,  Ithaca,  1912. 


ASTRONOMY,  METEOROLOGY,  AND  SEISMOLOGY.  19 

by  Pearson.1    From  this  frequency  polygon  it  appeared  that  the  curve  which 
most  nearly  fits  the  conditions  is  the  "  normal  curve  "  of  distribution.2 

It  can  be  shown  that  the  probability  of  occurrence  of  any  phenomenon  which 
follows  the  normal  distribution  may  be  determined  when  the  "standard  devi- 
ation" is  known.  By  the  use  of  the  standard  deviation  a  much  more  certain 
measure  of  occasional  occurrences  is  determined  than  is  possible  by  a  count 
of  the  two  or  three  extreme  occurrences  in  a  comparatively  short  record. 
Figure  6  shows  the  normal  frequency  curves  of  the  distributions  of  the  dates  of 
last  killing  frost  in  spring  for  five  stations  and  of  first  killing  frost  in  fall  for 
three  stations.  These  stations  were  selected  to  show  the  usual  dispersions  of 
the  normal  frequency  curves.  Each  curve  has  been  shaded  to  show  the  region 
within  which  9/10  of  these  dates  fall;  that  is,  the  shaded  area  is-9/10  of  the 
total  area  under  the  curve.  The  normal  concentration  of  last  (or  first) 
occurrence  of  killing  frost  at  any  given  number  of  days  after  (or  before)  the 
average  date  is  shown  by  the  height  of  the  curve  above  the  base  line  at  the 
place  where  this  number  appears  on  the  scale.  The  place  where  the  border  of 
the  shaded  area  cuts  the  base  line  shows  the  date  after  (or  before)  which 
killing  frost  will  occur  only  1  year  in  10  on  the  average.  By  counting  the 
cases  of  frosts  which  fall  within  the  dates  shown  on  the  smooth  normal  curves 
to  include  9/10  of  the  dates,  it  has  been  found  that  out  of  27,838  cases  of 
occurrence  of  last  killing  frost  in  spring  or  first  killing  frost  in  fall,  2,739 
occurred  later  in  spring  or  earlier  in  fall  than  the  dates  included  in  the 
shaded  area.  This  is  0.984  in  10,  which  is  a  very  close  agreement. 

1  Pearson,  K.  :  Skew  variation  in  homogeneous  material.  Phil,  trans.  Roy.  Soc.,  ser.  A, 
186  :  343-414,  London,  1895. 

*  The  following  explanation  of  the  method  of  obtaining  the  date  in  the  spring  after 
which,  and  that  in  the  autumn  before  which,  frost  will  occur  on  the  average  only 
1  year  in  10  has  been  prepared  by  Mr.  H.  R.  Tolley,  who  made  the  preliminary  mathe- 
matical studies  upon  which  this  statement  of  frost  risk  is  based  : 

When  the  problem  of  investigating  the  variability  of  these  dates,  and  consequently  the 
variability  of  the  length  of  the  growing  season,  first  presented  itself,  it  was  seen  that 
if  the  distribution  at  any  station  followed  the  normal  frequency  curve  (variously  known 
as  the  probability  curve,  the  curve  of  error,  etc.)  it  would  be  possible  to  determine  a 
spring  date  for  any  station  after  which  frost  would  occur  on  the  average  1  year  in  4, 
1  year  in  5,  or  1  year  in  100,  if  so  desired,  and  similar  dates  for  early  frosts  in  the  fall. 

Now,  owing  to  the  paucity  of  years  of  observations  at  any  one  station,  the  average  for 
all  stations  being  probably  less  than  20  years,  and  on  account  of  the  fact  that  in  the 
neighborhood  of  a  thousand  observations  are  necessary  to  obtain  a  smooth  curve,  33 
stations  distributed  over  the  whole  United  States,  with  records  varying  from  5  to  43 
years  in  length,  and  823  as  the  aggregate  number  of  years,  were  selected  and  combined, 
a  curve  was  made  for  the  combination  (see  fig.  5).  If  these  are  representative  stations, 
and  a  single  type  of  curve  is  to  be  selected  to  fit  every  individual  station,  it  will 
obviously  be  that  of  the  curve  of  best  fit  for  this  combination. 

The  criteria  developed  by  Karl  Pearson  in  "  Skew  Variation  in  Homogeneous  Material  " 
were  applied  to  the  observations  and  they  showed  that  while  the  curve  of  best  fit  was 
not  exactly  a  normal  curve,  it  was  similar  in  all  respects  except  for  a  very  slight  amount 
of  skewness  —  i.  e.,  the  mean  and  the  mode,  or  abscissa  of  the  highest  point  of  the  curve, 
did  not  coincide.  The  distance  between  them,  however,  was  less  than  one  day,  and 
since  the  unit  of  measurement  is  one  day  and  it  is  impossible  to  consider  in  the  final 
results  anything  less  than  that,  it  was  finally  decided  to  use  the  constants  of  the  normal 
curve  in  the  computations,  and  the  results  seem  to  have  justified  this  selection. 

-12 

The  equation  of  the  normal  curve  is  y=y«e  2ffZ  ,  the  origin  being  at  the  mean,  and  the 
ordinate  at  that  point  being  y0.  a  is  the  square  root  of  the  arithmetic  mean  of  the 


squares  of  all  the  deviations  from  the  average  date  (~)       and  is  commoilly  known 

as  the  standard  deviation.  The  y  (ordinate)  of  any  point  represents  the  number  of 
occurrences  of  the  particular  deviation,  x,  to  which  it  corresponds,  and  the  total  number 
of  deviations  (or  observations)  is  the  area  of  the  curve.  It  was  found  by  referring  to  a 
table  of  the  probability  integral,  which  is  the  integral  of  the  equation  to  this  curve 
that  nine-tenths  of  the  area  lies  before  the  ordinate  whose  abscissa  is  1.28  *. 


20 


PROCEEDINGS   SECOND   PAN   AMERICAN   SCIENTIFIC   CONGRESS. 


FREQUENCY  CURVES 

LAST  SPRING  FROST-FIRST  AUTUMN  FROST 


AUTUMN 
AV.DATE  NO  V.I 


HASKELL.TEX. 
ff-7.7 


AUTUMN 
AV.DATEOCTI2. 


LEWISB'JRG.PA. 


SPRING 
AV.  DATE  APR.I5 


NEW  BEDFORD 
MASS. 
ff-IO.O 


It  has  also  been  found  that  in  individual  cases  there  is  rarely  more  than 
one  unit  variation.  For  example,  from  a  station  with  a  record  of  36  years  there 
are  practically  never  more  than  five  dates  of  last  killing  frost  in  spring'or 
five  of  the  first  killing  frosts  in  fall  which  fall  beyond  the  date  shown  by 
the  smooth  curve,  and  practically  never  less  than  two.  In  a  great  majority  of 
cases  the  number  for  such  a  record  is  three  or  four.  This  apparently  shows 
that  the  normal  curve  is  a  better  indication  of  the  frost  probabilities  than  any 
count  of  the  actual  cases,  which  is  what  we  should  expect  from  a  mathematical 
consideration  of  the  situation.  The  counting  of  a  large  number  of  cases  shows 
that  these  extreme  frost  dates  follow  very  closely  the  normal  distribution. 
From  that  the  inference  is  strong  that  for  any  individual  station  the  distribu- 
tion is  normal  provided  tliere  is  a  long  enough  record.  The  normal  distribution 
determined  from  the  actual  distribution  for  the  period  of  the  record  may  be 

used  to  show  the  probability  of  the  occurrence 
of  the  last  killing  frost  in  spring  or  the  first 
killing  frost  in  fall.  The  probable  error  -of  the 
standard  deviation  of  the  date  of  last  killing 
frost  was  calculated  for  several  stations  from  ob- 
servations covering  a  period  of  20  years  or  more, 
and  was  found  to  vary  from  two  to  five  days,  de- 
pending upon  the  length  of  record  and  also  upon 
the  range  of  variation.  The  probable  error  of  the 
standard  deviation  and,  hence,  of  the  dates  deter- 
mined, varies  directly  with  the  magnitude  of  the 
standard  deviation  and  inversely  as  V™  where  n 
is  the  number  of  observations.1  Of  course,  the 
number  of  observations  for  a  single  station  is  so 
small  that  the  standard  deviation  can  not  be  re- 
garded as  well  established,  but  it  is  significant 
that  the  combination  of  many  records  results  in 
a  nearly  smooth  curve  with  a  single  mode  and 
that  the  successive  addition  of  more  observations 
makes  the  curve  smoother  and  smoother. 

If  the  normal  curve,  or  rather  the  standard  de- 
viation, could  be  determined  for  each  of  the  800 
or  more  stations  in  the  United  States  having 
records  sufficiently  long  to  justify  this  procedure, 
it  would  be  possible  to  show  the  risk  of  frost  at 
any  particular  date.  However,  the  clerical  labor. 
involved  in  determining  standard  deviations  for  a 
large  number  of  stations  is  so  great  that  this 
has  been  determined  only  for  569  selected  stations.  The  standard  deviations  for 
these  stations  are  given  in  Table  2  for  both  spring  and  fall  frosts,  together 
with  the  average  dates  of  last  killing  frost  in  spring  and  of  first  killing  frost 
in  fall. 

This  method  of  determining  the  probability  of  frost  is  subject  to  limitations 
because  .of  the  small  number  of  observations  in  any  case.  As  has  been  pointed 
out,  there  are  seldom  more  than  40  observations  and  more  often  20  to  25. 
This  means  that  it  is  not  possible  to  obtain  a  measure  of  dispersion  which  is 
not  subject  to  considerable  error. 


AUTUMN 
AV.DATE  SEPT.  19. 


B'SMARCK.N.0. 
041.0 


v      SPRING 
AV.DATEAPRI3. 


SPRING 
AV.  DATE  FE  8.25 


SPRING 
AV.DATEMAR.20. 


LLANO.TEX. 
ff-Si.2 


AV.DATE  MAY 23. 


ROSALIA.WASH. 
G-2S.S 


DEVIA.   1*5    30     15     0     15    30    <»S     DAYS 


FlQ.  6. 


iThe  mathematical  statement  is  £*=  ±0.674-p-where  E<r  is  the  probable. error  of  the  standard  devia- 
ion,  a,  and  n  is  the  number  of  observations. 


ASTRONOMY,  METEOROLOGY,  AND  SEISMOLOGY. 


21 


However,  as  the  years  of  observation  increase,  the  accuracy  of  the  method 
will  become  greater,  and  even  with  these  limitations  it  is  probable  that  the 
date  obtained  is  more  accurate  than  that  which  results  from  a  count  of  cases, 
because  the  date  obtained  by  the  use  of  the  standard  deviation  rests  on  20 
observations  for  20-year  records  and  40  observations  for  40-year  records,  while 
those  obtained  by  noting  extreme  cases  rest  on  two  occurrences  in  the  case  of 
20-year  records  and  four  occurrences  in  the  case  of  40-year  records. 


TABLE  2. — Frost  data  for  selected  stations. 


Station. 

County. 

H. 

Years 

A.. 

ffe. 

A». 

0». 

Alabama: 
Bermuda  

Conecuh  

27 

March,  21  .2..., 

15.9 

November,  6.0 

10  0 

Daphne 

Baldwin  j 

22 

March,  3.4    . 

14.5 

November  22  9 

14  4 

Eufaula  

Barbour  

200 

22 

March,  Hi.l  

17.4 

November,  9.3  

13.3 

Florence..  .     . 

Lauderdale  . 

620 

27 

March,  30.5  

15.1 

October  28  5 

8  9 

Gadsen 

Etowah 

621 

24 

April  1  7 

H  3 

October  29  5 

11  7 

Highland  Home 

Crenshaw  .  .  . 

22 

March,  8.5  

13.0 

November,  15.1 

11  4 

Livingston 

Sumter 

1(>0 

22 

March  20  4 

13  4 

Novrmbrr  1  6 

10  7 

Opelika 

Lee 

917 

23 

March  20  6 

12  4 

Novemoer  12  2 

15  7 

Tuscaloosa  

Tuscaloosa.. 

230 

25 

March,  28.2  

13.2 

November  5.4 

10  3 

TJniontown 

Perry 

273 

26 

March,  16.4 

13.7 

November  10  1 

12  2 

Valley  Head.... 

Dekalb  

1,031 

26 

April,  9.0  

13.9 

October,  21.6 

10.3 

Arizona: 
Bishee 

Cochise 

5  500 

22 

March  21  6 

22.8 

November  25  7 

12  8 

Buckeye  

Maricopa..  . 

980 

20 

March,  5.9  

20.4 

November,  25.2  

18  3 

Dudleyville 

Pinal 

2,300 

22 

March  30.0     .  . 

16.6 

November  11  3 

13  4 

Fort  Grant  

Graham...  . 

4,916 

31 

March,  16.2  

22.6 

November,  25.5  

17.0 

Fort  McDowell 

Maricopa.. 

1,450 

20 

March,  9.7  

29.6 

November,  21.7 

21  4 

Fort  Mohave 

Mohave 

604 

23 

February,  6.5 

21.5 

December  10  6 

23  5 

Holbrook  

Navajo  

5,500 

25 

Mav,  5.7  

15.1 

October,  15.3    .  ... 

12  5 

Jerome 

•  Yavapai 

4,743 

17 

March,  15.7  . 

22.7 

November  26  7 

17  1 

Oracle 

Pinal 

4  500 

21 

March  9  4 

19  1 

December  3  6 

12  6 

Parker  .. 

Yuma  .. 

353 

18 

March,  7.3  

19.7 

November,  22.1 

12  0 

Phoenix  Exper- 

Maricopa 

1  092 

21 

March  7  8 

17  7 

November  27  6 

15  0 

iment      Sta- 
tion. 
Tucson 

Pima 

2  427 

24 

March  13  2 

19  9 

November  24  1 

17  2 

Yuma  

Yuma...  . 

141 

37 

January1  (29),  19.7. 

25.0 

December  »(29),  21.7 

22.8 

Arkansas: 
Camden  

Ouchita  

158 

23 

March,  22.0... 

16.6 

November,  3.3  

13.6 

Con  way 

Faulkner. 

309 

23 

March,  25.6  

12  1 

November,  1.0 

10  3 

Corning 

Clav 

293 

21 

\pril  1  5 

10  8 

October  17  6 

11  7 

Fort  Smith  

Sebastian  

481 

33 

March,  21.2...'.  

11.4 

November,  5.8  

10.6 

Newport 

J  ad  'son 

231 

26 

March,  25.3    . 

11.1 

October  25.7 

9  9 

Helena  

Phillips  

182 

23 

March,  21.6  

14.2 

November,  5.5  

10.1 

Malvern 

Hot  Spring. 

277 

24 

April,  30  :  

12.2 

October,  29.9    

9.6 

Rogers 

Ben  ton 

1  385 

22 

\pril  11  6 

11  5 

October  20  5 

9  0 

Stuttgart 

Arkansas 

228 

23 

March  273 

13  1 

October  28  5 

11  8 

Texarkana 

Miller 

332 

23 

March,  20.6  

13.2 

November,  8.0 

11  i 

California: 
Berkeley  

Alameda 

320 

27 

January1  (18),  17.8. 

28.5 

January1  (17),  3.0.  . 

23.3 

Cedarville 

Modoc 

4  675 

20 

Mav  23  1     . 

18.0 

September,  26.0 

12.0 

Chino 

San  Bernar- 

714 

21 

February  14  0 

22  6 

December  13  3 

23  0 

Claremont  
Durham  

dino. 
Los  Angeles. 
Bntte 

1,200 
160 

26 
20 

February,  11.7  
March,  13.6  

9.3 

26.4 

December,  20.3  
November,  2.3  

25.9 
17.4 

Escondido 

San  Diego 

650 

20 

March,  27.3  

27.7 

November,  19.8  

29.8 

•Georgetown 

Eldorado 

2  650 

26 

April   1  5 

29  7 

November  16.2 

17.8 

Hollister  . 

San  Benito 

284 

20 

March,  14.7  

37.9 

November,  16.1  

15.5 

Iowa  Hill 

Placer 

2  825 

21 

March,  26.2  

25.0 

December,  5.2  

19.4 

Kennedy  Gold 

A  mad  or 

1  500 

21 

March  13  7 

33  0 

December,  7.5    . 

14  7 

Mine. 
Lick    Observa- 

Santa Clara 

4  209 

•     25 

Mav.  7  1  .. 

26.9 

November,  16.0  

23.5 

tory. 
Lodi. 

San  Joaquin 

35 

22 

March,  4.0  

21.0 

November,  22.8  

19.1 

Los  Gatos  
Mammoth  Tank 

Santa  Clara. 
Imperial 

600 
257 

20 
20 

February  •»  (18),  3.6. 
Februarv,7.1    . 

24.8 
30  7 

December  «(  17),  23.4 
December,  30.0  

23.7 
36.2 

Nevada  City 

Nevada 

2  580 

22 

Mav  3  4 

17  8 

October  23  4 

16.7 

Napa.....  ..."."I 
Oroville  

Napa  
Butte  

'   60 
250 

24 
21 

February,  22.4  
February,  9.0  

10.4 
37.4 

December,  16.0  
December,  6.8  

29.4 
13.8 

Palermo 

do 

213 

23 

March,  11.7  

26.2 

November,  21.7  

16.0 

Placerville 

Eldorado 

1.820 

23 

April,  5.3  

27.0 

November,  3.1  

19.2 

Reddin" 

Shasta 

552 

24 

March,  9  8    . 

26.7 

December,  2.3  

18.7 

Tlepressa 

Sacramento 

305 

22 

February  '  (18),  20.6 

9.8 

December  »(  19),  13.4 

14.0 

Riverside 

Riverside 

851 

27 

February  >  (26),  24.2 

27.7 

December  K23),  8.2. 

21.3 

Sacramento  

Sacramento. 

71 

32 

February  »  (31),  10.5 

29.6 

November  '(30),  27.6 

19.8 

tSome  years  are  frost  free.  The  number  in  parentheses  is  the  number  of  years  in  which  frost  occurred. 
J  or  example,  at  Yuma  the  record  covers  37  years,  of  which  8  were  frost  free  and  29  had  frost.  For  a  method 
<  I  determining  the  frost  risk  under  such  conditions,  see  Table  3,  p.  621. 


PROCEEDINGS  SECOND  PAN  AMERICAN   SCIENTIFIC   CONGRESS, 


TABLE  2. — Frost  data  for  selected  stations — Continued. 


woH 


Station. 

County. 

H. 

Years. 

iifll  nr.Ai.  DJinirj 

. 

<r.. 

Aa. 

a*. 

California—  Contd. 

1  054 

24 

March  13  6 

984 

November,  26.5 

>2<jo 
14  8 

. 

dino. 
Riverside 

1  550 

22 

March,  18.2.  . 

24.2 

November,  23.6  

19.7 

Santa  Barbara.. 
Santa  Cruz 

Santa    Bar- 
bara. 
Santa  Cruz 

'130 
20 

26 
21 

February  i(7),  1.1.. 
March,  14.8  ... 

38.3 
26.9 

December  i(7),  15.1. 
December,  4.1  

22.4 
19.3 

Shasta 

Shasta 

1  148 

20 

April,  2  5 

31.3 

November,  18.0 

22  8 

Stockton  

San  Joaquin 

23 

22 

February  1(20),  9.6. 

29.2 

November  i(21),  26.2 

11.8 

Lassen 

4  195 

18 

May,  12.5 

19.3 

October,  6.1  

26.5 

Ukiah 

Mendocino  . 

630 

22 

April,  2.0  

31.0 

November,  10.2  

20.4 

Upper  Lake 

Lake 

1  350 

22 

March,  31.4  

16.7 

November,  6.4  

18.3 

Wheatland 

Yuba  

84 

26 

February,  26.2  

25.5 

December,  2.0  

16.0 

Willow 

Glenn 

136 

20 

March,  2.1  

30.6 

November,  28.4  

8.7 

Colorado: 
Breckenridge 

Summit 

9  536 

20 

Julv  15  1 

11.9 

August,  18  6 

13  9 

Canon  City 

Fremont 

5  343 

22 

April,  27.0      

12.2 

October,  11.1  

14.3 

Castle  Rock 

Douglas  

6,220 

20 

Mav,  12.8  

12.1 

September,  21.6  

25.3 

ColoradoSprings 

El  Paso 

6  098 

22 

May  5  4 

9.7 

October  1  0 

12  4 

Delta 

5'  025 

20 

May,  10.8  

13.4 

September,  27.0  

12.0 

Denver 

Denver  

5,272 

43 

Mav,3.9  

12.3 

October,  6.8  

11.5 

Fort  Collins  

Larimer  

4,985 

20 

Mav,  4.2  

10.5 

September,  25.6.... 

10.3 

Greelev 

Weld 

4  649 

20 

April,  29  2 

10.2 

October,  1.0  

13.0 

Grand  Junction 

4  602 

23 

April  17  7 

12.7 

October,  17.9 

14  4 

Grand  Valley 

Garfield 

5  089 

20 

Mav,  2.8  

13.8 

September,  29.7  

13.2 

Gunnison 

7  670 

22 

June  28  2     . 

13.0 

August,  31.1 

12  3 

Lake  Moraine 

El  Paso... 

10,265 

21 

June.  19.6  

19.1 

September,  8.4  

12.0 

Las  Animas 

Bent 

3  899 

22 

April,  279      

11.0 

October,  5.8  

12.8 

Lay 

Moffat  

6,190 

20 

June,  11.6  

26.2 

September,  4.2  

13.2 

Leroy 

Logan 

4  380 

20 

May,  1.8  

12.0 

September,  30.8  

13.6 

Meeker  (near) 

Rio  Blanco 

6  182 

21 

June,  12  6 

13.2 

September,  11.3  ... 

10.7 

Pagoda 

Routt  

6,500 

19 

June.  16.5  

15.5 

September,  6.3  

8.7 

Pueblo 

Pueblo 

4  685 

27 

April,  26  5         

8.9 

October,  7.4  

8.8 

Sagauche 

7  745 

19 

May,  25  3 

13.6 

September,  25  4 

10  4 

San  Luis 

Costilla 

7,794 

22 

June,  6.7  

11.0 

September,  20.8  

11.6 

Connecticut: 
Canton 

Hartford 

900 

30 

May  60 

11  9 

October  3  5 

8  3 

New  Haven 

New  Haven 

117 

42 

April,  16.8 

10.2 

October,  21.3  

9.2 

Waterbury 

do 

400 

28 

April  30  8 

9  8 

October,  6  8 

11  1 

Delaware: 
Millsboro 

Sussex 

20 

22 

April,  21  5 

11.1 

October,  20.3  .  .  . 

8.7 

Florida: 
Brooksville  
Jacksonville 

Hernando.  .  . 
Duval 

126 
222 

23 
58 

February  i  (20),  16.1. 
February  14  6 

24.8 
27.5 

December  i(20)  ,16.1. 
December,  6  3 

22.4 
17  1 

Kissimmee 

Osceola     ... 

65 

23 

February1  (19),  2.5. 

20.8 

December  1  (19)  ,26.3  . 

19.6 

Lake  City 

Columbia 

210 

24 

March  6'  3 

16.2 

November,  30  0 

15.0 

Pensacola 

Escambia  .  .  . 

140 

36 

February,  23.3  

21.0 

December,  9.4  

24.0 

St.  Augustine... 
Tallahassee 

St.  Johns  .  .  . 
Leon 

10 
192 

23 
25 

Februarv  1  (22),  18.  2 
March  10 

18.9 
20  3 

December  i(22),  21.9 
December  2  5 

20.6 
19.0 

Georgia: 
Blakeley 

Early 

300 

23 

17  2 

10  1 

Gillsville".  !  '.'.'.'.'. 

Hall.."."."!!!! 

1,052 

22 

April,  5.7     

8.5 

October,  24.3.'..*.!!! 

12.3 

Hawkinsville 

Pulaski 

235 

22 

March,  246     

16.6 

November,  5.6  

12.7 

Louisville 

Jefferson 

259 

24 

March  26  8 

15  0 

November,  58. 

12.7 

Milledgeville 

Baldwin  

276 

21 

March,  29.2     

12.4 

November,  4.0  

12.5 

Monticello 

Jaspar 

800 

22 

March  27  0 

12.6 

November,  3  6 

12.0 

Point  Peter  ... 

Oglethorpe.. 

600 

25 

April,  1.4     

9.4 

October,  30.6  

11.7 

Poulan  

Worth.. 

365 

25 

March,  20  0       ... 

17.2 

November,  7.2  

11.2 

Quitman 

Brooks 

173 

23 

March  17  6 

17.7 

November,  15  4 

13.5 

Ramhurst  

Murray  .  .  . 

900 

21 

April,  15.5      

13.3 

October,  18.2  

9.7 

Rome  

Floyd    .... 

576 

23 

Zil,  87 

9.4 

October,  25.5  

8.5 

Talbotton 

Talbot 

750 

22 

ch  30  7 

12  4 

November,  3  8 

12.1 

Idaho: 
American  Falls 

Power  .... 

4  341 

20 

May  204 

20.1 

September,  118  

12.4 

Boise 

Ada 

2  739 

April  26  1 

17  1 

October  14  3 

13.3 

Lewiston  

Nez  Perce  .. 

757 

21 

April.  63^ 

14.1 

October,  26.9  

17.7 

Moscow  .  .  . 

Latah 

2  748 

21 

May  5  9 

15  5 

October  8  4 

17.2 

Oakley 

Cassia 

4  700 

21 

May  23  5 

17  8 

September  19  1 

12.5 

Pavette  

Canyon  

2,159 

23 

May,  4  6 

18.6 

September,  28.5  

10.9 

Pofthill.    . 

Boundary 

1  665 

21 

Mav  10  1 

19  2 

September,  27  9 

10.7 

Illinois: 
Albion  

Edwards  ... 

531 

21 

April,  13.8 

10.2 

October,  21.5  

10.1 

Aurora  

Kane   .  . 

678 

27 

May  4  7 

13  9 

October  74 

11.4 

Carlinville  

Macoupin  .  .  . 

663 

22 

April,  21.4     

10.6 

October,  14.9  

10.6 

Charleston  

Coles  

720 

17 

April,  28  4 

13.7 

October,  14.4 

11.4 

Decatur  

Macon  .  .  . 

685 

21 

April  23  0 

11  3 

October  15  9 

10.9 

Dixon  

Lee  

725 

22 

April,  28.8      

11.8 

October,  10.6  

12.4 

Galva 

Henry 

842 

22 

^pril  29  9 

13  4 

October  11  8 

10  3 

Havana... 

Mason... 

475 

21 

April,  19.0  

13.0 

October!  17.3... 

10.3 

i  Some  years  are  frost  free.  The  numbers  in  parentheses  are  the  years  in  which  frost  has  been  recorded 
e.  g.,  at  Brooksville  there  are  23  years  of  record,  of  which  4  were  frost  free  and  19  had  frost.  For  a  method  of 
determining  the  frost  risk  under  such  conditions,  see  Table  3,  p.  621. 


ASTRONOMY,  METEOROLOGY,  AND  SEISMOLOGY. 
8  -IDS   JlADIflSMA   tfAl  dTCOOaa  '  BOT£I<I330OS«I 

TABLE  2.  —  Frost  data  for  selected  stations  —  Continued. 

• 


23 


Station. 

County. 

H. 

Years. 

A.. 

... 

A.. 

... 

Illinois—  Contd. 
La  Harpe     

Hancock  

698 

20 

April,  24.7... 

10.1 

October,  5.0  

13.7 

Mount  Vernon 

Jefferson 

511 

20 

April,  19  6     .  . 

12.6 

October,  17.2 

11.9 

New  Burnside 

Johnson 

613 

20 

April  18  5 

12.9 

October  16  6 

10  § 

Ottawa  

LaSalle    ... 

500 

22 

April,  26.2      

10.9 

October,  12.2  

11.7 

Peoria 

Peoria 

519 

59 

April,  15  1 

10.2 

October,  19  0 

9.8 

Philo 

Champaign 

700 

23 

April  30  7 

14.3 

October  3  8 

13  2 

Streator  

La  Salle 

626 

22 

April.  29.9... 

12.9 

October,  11.0  

12.2 

Winnebago 

Winnebago 

900 

21 

May,  7.4 

13.3 

October,  5  8 

11.6 

Indiana: 
Columbus  .  . 

Bartholo- 

632 

22 

April  27.9  

12.7 

October  10.4. 

12.2 

Connersville  .  . 

mew. 
Fayette.  . 

844 

22 

April,  30.2  

14.0 

October,  8.8  

12.9 

Farmland 

Randolph 

1  101 

22 

April  25  1 

14  0 

October  14.5 

11.7 

Hammond  

Lake.  .  . 

598 

22 

April  27.0  

11.5 

October,  15.3  

11.7 

Huntington 

Huntington 

462 

21 

May,  2.5     . 

14.1 

October  9.6 

12.4 

Kokomo  

Howard..    . 

976 

22 

April,  29.6  

16.4 

October,  3.6  

12.4 

Lafayette 

Tippecanoe 

661 

22 

April  26  8 

13.9 

October  7.3 

12.4 

Logansport  .  .  . 

Cass  

620 

23 

April,  26.9  

13.5 

October,  13.4  

12.8 

Marengo  . 

Crawford 

363 

22 

April  22.0. 

13.7 

October  10.0    . 

13.9 

Mount  Vernon  . 

Posey  

410 

22 

April,  14.7  

12.2 

October.  20.4  

10.0 

Rockville. 

Parke 

722 

22 

April  26.0.  . 

13.3 

October,  10.1  .    .  . 

12:7 

South  Bend 

St  Joseph 

726 

21 

Mav  5  9 

13  0 

October  12.8 

12.2 

Vevay. 

Switzerland 

525 

27 

April  21.2... 

11.3 

October.  23.6  

12.0 

Vincennes 

Knox 

431 

21 

April  13  5 

11  2 

October  20  2 

14  1 

Iowa: 
Algona 

Kossuth 

1  213 

22 

Mav,  1.4  .  . 

10  3 

October,  4.9         .  . 

9  3 

Bonaparte.. 

Van  Buren.. 

22 

April,  23.6  

10.3 

October,  9.8  

11.0 

Carroll. 

Carroll 

1  260 

22 

April  308 

10  8 

October,  4.4 

13.9 

Corning  

Adams... 

1,117 

22 

April  29.7  

11.8 

October,  7.2  

11.8 

Des  MoLies 

Polk 

861 

37 

April,  22  2  . 

14  4 

October,  10.5  

11.9 

Keokuk  

Lee... 

614 

43 

April,  14.3  

11.7 

October,  15.1  :. 

12.3 

Osage.  . 

Mitchell 

1,184 

22 

May  1.9...  . 

17.7 

October  3.2      

10.4 

Kansas: 
Ashland    . 

Clark.... 

1,951 

26 

April,  16.2  

19.8 

October,  20.7  

12.0 

Atchison 

Atchison 

973 

23 

April  11  2 

14  0 

October,  15.8    .  .  . 

12.0 

Burlington  .  .  . 

Coffey..'. 

1,010 

21 

April  16.7  

15.4 

October,  15.0  

11.4 

Colby 

Thomas 

3  138 

22 

Mav  1  2 

11  8 

October,  5.5  

13.2 

Columbus 

Cherokee 

898 

24 

April  6  2 

12  3 

October  22  0 

9  9 

Cunningham 

Kingman 

1  680 

20 

April  208.. 

15  7 

October,  17.0  

12.2 

Dodge  City  

Ford  . 

2,513 

40 

April.  18.5  

12.6 

October,  17.7  

9.6 

Ellinwood 

Barton 

,790 

20 

April  25  0... 

13  4 

October,  16.6  

12.6 

Emporia 

Lyon 

138 

24 

April  10  5 

15  9 

October,  18.1 

12  2 

Frankfort  

Marshall 

146 

20 

April,  22.9  .. 

13.4 

October,  10.8  

12.5 

Garden  City 

Finney 

836 

21 

April  28  7 

13  7 

October,  10.0       .  . 

13.4 

Grenola... 

Elk 

116 

22 

April,  15.2... 

13.4 

October,  18.1  

10.0 

Hutchinson 

Reno 

535 

23 

April  14  6 

13  9 

October,  16.2      

10.5 

Horton  . 

Brown 

188 

25 

April,  18.6  

11.4 

October,  15.0  

10.8 

Independence 

Montgomery 

800 

38 

April  13  8 

16  1 

October,  22.3    

12.9 

Lebo  

Coffey  . 

,138 

22 

April.  14.3  

14.5 

October,  18.4  

9.5 

Me  Pherson 

Me  Pherson 

495 

23 

April  21  3  .. 

12  6 

October,  16.1  

12.0 

Macksville 

Stafford 

2  0°2 

22 

April  26  3 

15  9 

October  13.2 

12  1 

Manhattan  (Ag- 

Riley 

I'lOO 

25 

April'  25  1. 

14.0 

October,  11.9  

11.2 

ricTColK 
O  lathe 

1  032 

22 

April  21  7 

14  6 

October,  15.1 

11.6 

Oswego 

Labette 

899 

23 

April  13  5 

16  1 

October,  22.4    

12.6 

Sedan.. 

Chautauqua 

834 

25 

April  12.3  

15.0 

October,  26.0  

14.3 

Topeka 

Shawnee 

997 

28 

April  93 

17  2 

October,  15.1  

10.7 

Wichita  . 

Sedgwick 

1,377 

27 

April  10.0  

13.3 

October,  19.8  

12.3 

Kentucky: 
Blandville 

Ballard 

445 

21 

April  11  4 

11  6 

October,  19.7  

9.8 

500 

22 

April  17  6 

10  7 

October,  18.1    .  .  . 

8.5 

Earlineton 

Hopkins 

370 

20 

April,  13  8 

9.7 

October,  18.0  

10.3 

Eubank 

Pulaski 

1  177 

20 

April  22  8 

10  2 

October,  14.2    .  .  . 

11.3 

Mount  Sterling 

Montgomery 

'930 

22 

April'  16.4  .. 

10.6 

October,  17.4  

9.3 

Shelbyville 

Shelby 

759 

22 

April'  18  7 

9  7 

October,  16.4.     ..  . 

9.1 

Louisiana: 

Rapid  es 

77 

23 

March  12  4 

17  2 

November,  6  4 

13  7 

Amite.  . 

Taneipahoa 

130 

22 

March,  14.2  

15.5 

November,  4.8     .  . 

10.8 

Donaldson  ville 

Ascension 

33 

22 

Februarv,  26.5  

16.0 

November,  23.0. 

14.9 

Liberty  Hill 

24 

March  23  1... 

15.9 

November,  3.8.  . 

12.2 

Melville 

St  Landry 

45 

21 

March  10  5 

19  2 

November,  5.0.  . 

11.7 

Monroe 

Ouachita 

82 

22 

March,  13.5  

13.1 

November,  10.6. 

16.5 

Opelousas 

St  Landry 

83 

22 

March  84 

13.8 

November,  12.0. 

11.2 

Plain  Dealing 

Bossier 

268 

21 

March,  25.5  

16.0 

November,  5.2  .  . 

11.5 

SuEartown 

Calcasieu 

21 

March  65. 

17.2 

November,  18.3. 

13.1 

Maine: 
Bar  Harbor 

20 

25 

Mav  11  8 

13.7 

October,  8.2  

14.8 

Cornish 

York 

784 

40 

May  1  4 

14  4 

October  2.6 

9.7 

Washington 

76 

42 

April  279 

8.0 

October,  23.1  

10.7 

Farmineton  .  .  . 

Franklin  

450 

25 

Mav.  17.6.... 

12.8 

September,  20.4  .  .  . 

10.2 

24  PROCEEDINGS   SECOND  PAN   AMERICAN   SCIENTIFIC   CONGRESS. 

TABLE  2. — Frost  data  for  selected  stations — Continued. 


Station. 

County. 

H. 

Years 

A.. 

a*. 

Aa. 

*a. 

Maryland: 
Annapolis  

Baltimore  
Cumberland... 
Emmitsburg... 
Fallston  
Fort  McHenry 
Frederick  
Great  Falls  .... 
New  Market... 
Washington  .  .  . 
Woodstock.... 
Massachusetts: 
Blue   Hill  Ob- 
servatory. 
Concord 

Anne  Arun- 
del. 
Baltimore... 
Allesrany... 
Frederick.. 
Harford  
Baltimore.. 
Frederick  .  . 
Montgomery 
Frederick.. 
D.C.... 

145 

115 
623 
720 
450 
36 
275 
200 
550 
112 
392 

640 

139 
53 
420 
88 
40 
298 
711 

609 
686 
1,246 
707 

"'955' 
858 

614 
975 

1,039 
1,179 
863 
1,299 
1,175 
935 
1,510 
1,251 
614 
1,300 
917 

28 
424 

500 
126 
437 
446 
206 

853 
1,200 
v   982 
1,280 
925 
1,265 
864 
797 
1,480 
1,023 
1,072 

5,200 

4,900 
5,716 
3,100 
3,041 
2,630 
2,069 
3,350 
2,487 

4,110  : 

2,371 
3,225 
2,020 
5,000 

22 

42 
29 
35 
36 
22 
26 
31 
25 
43 
41 

28 

29 
28 
27 
39 
42 
40 
40 

40 
20 
22 
31 
21 
35 
21 

27 
35 

25 
22 

25 
22 
23 
34 
21 
28 
21 
28 
19 

21 
22 

23 
24 
24 
22 
22 

25 
22 
31 
23 
24 
27 
25 
36 
22 
23 
22 

20 

21 
20 
20 
34 
25 
24 
23 
33 
35 

23 
23 
29 
21 

April  16  0 

14.8 

15.3 
13.0 
10.7 

13.9 
'   10.8 
!  14.3 
13.7 
14.7 
11.1 
11.8 

10.9 

9.0 
12.4 
10.6 
10.0 
13.2 
13  5 
10.7 

11.1 
11.2 
13.7 
13.7 
16.5 
13.3 

October,  31.9  

November,  4.6  
October,  21.5 

12.4 

12.6 
15.5 
10.8 
9.5 
14.0 
12.2 
10.0 
11.6 
10.5 
9.7 

10.5 

13.3 
7.5 
11.2 

12.0 
9.5 
13.9 
9.8 

12.0 

10.4 
10.5 
15.5 
12.2 
15.2 
11.6 

10.2 
13.3 

12.9 
12.6 
11.8 
10.5 
11.8 
13.6 
11.8 
10.6 
9.4 
9.7 
10.3 

14.6 
7.5 

11.1 
10.7 
7.6 
9.5 
13.9 

10.3 
11.5 
11.0 
10.3 
12.8 
9.1 
13.3 
12.6 
15.0 
12.6 
11.9 

17.8 

16.4 
10.6 
18.7 
15.6 
14.2 
11.7 
12.7 
11.5 
15.1 

11.8 
19.8 
10.6 
13.4 

April  4  0 

April,  14.5...  . 

April  103    . 

October  27  1 

April  20.6  

October,  20.7  .  . 

April  12.0.. 

November,  10.1  
October  24  8 

April  17  7 

April  17.5... 

October,  19.1  
October,  22.0  
October,  22.3  
October,  14.5  

October,  12.7  

October,  2.0  
September,  29.4  .  .  . 
September,  23.6... 
j  October,  27.5  
October  16  8 

April  18  8 

April  8.7... 

Baltimore.. 
Norfolk  

Middlesex.. 
Plymouth.. 
Hampden.  . 
Bristol  
Bristol  
Worcester.  .  . 
Berkshire  .  . 

Alpena  
Ottawa  
Houghton... 
Kent...  
Kalkaska.  .. 
Kalamnzoo.. 
Grand  Trav- 
erse. 
Chippewa... 
Lapeer  

April  16  1 

April,  28.4      . 

May,  8.1.. 
May,  12.2... 
May,  13.7...      ... 

Middleboro  
Monson... 

New  Bedford... 
Somerset 

April,  14.3 

April  200 

Westboro 

May,  6.6.  . 

October,  3.1  
October  9  2 

Williamstown  .  . 
Michigan: 
Alpena  
Berlin  

May,  2  3 

May,  13.2 

September,  29.0... 
October,  4.6  

May,  17.5.  .  . 

Calumet 

May,  13.8  

October,  6.8  . 

Grand  Rapids  .  . 
Ivan 

Ap'il,  25  5 

October,  13.2  
September,  23.7... 
October,  21.7  

Mny  25  2 

Kalamnzoo  .  .  . 
Old  "Mission.... 

Sault  Ste.  Marie. 
Thornville  
Minnesota: 
Bird  Island  
Caledonia 

April,  26.6.... 

May,  12.1  

12.8 

9.8 
14.9 

12.8 
12.6 
12.1 
14.3 
13.3 
14.5 
10.6 
12.8 
13.1 
13.1 
13.5 

16.6 
13.5 

17.5 
15.6 
11.6 
11.9 
16.2 

12.8 
10.6 
11.6 
13.1 
14.9 
12.4 
13.2 
10.0 
12.7 
11.7 
11.4 

15.0 

20.0 
19.1  1 
16.1 
14.4 
16.8 
11.0 
12.2 
11.2 
13.3 

10.8 
17.0 
12.2 
1C.  3 

October,  19.3  

May,  14  3 

September,  27.6... 
October,  11.9  

September,  28.4  .  .  . 
October,  3.3  j  
September,  22.1  
September,  22.2  
September,  25.0  
September,  23.2.... 
September,  12.*  
September,  17.6  
September,  25.4  .... 
September,  27.6  
September,  27.3.... 

November,  28.7.  ... 
November,  5.0  

November,  5.6  
November  7  9 

April,  26.6  

Renville  
Houston  
Polk 

May,  11.4.. 

May,  4.2.  . 

Crookston 

May,  16  6 

Long  Prairie  
Lynd.  . 

Todd  .  .  . 

May,  18.2.  .. 

Lyon 

May,  14.8 

Moor  head  
Mount  Iron  
Pine  <River*Dam 
Two  Harbors. 

Hay  

St.  Loris.... 
Crow  Wing.. 
Lake  

May,  13.4  

June,  1.2.  . 

May,  16.0  

May,  20.7.  . 

Winnibieoshish 
Zumbrota  

Itasca  . 

May,  11  7 

Goodhue  

Hancock  .  .  . 
Oktibbeha.. 

Lincoln  
Washington. 
Attala 

May,  14.3  

Mississippi: 
Bay  St.  Louis... 
Agric  u  1  1  u  r  a  1 
College. 
Brookhaven  
Greenvillo  .  . 

February,  24.4  
March,  26.3. 

March,  18.0.... 

March,  19.0  
March  28  1 

Kosciusko 

October  29  1 

Lake 

Scott 

March  24  4 

October  29  1 

Natchez.. 

Adams 

March,  11  9 

November,  14.7.  .  .. 
October  16.5.  ... 

Missouri: 
Appleton  City.. 

Conception  
Houston  

St.Clair  
Shannon  
Nodaway  .  .  . 
Texas.  . 

April,  20.0      . 

April  13  5 

October  18  2 

April,  19.0.... 

October,  19.5  

April,  24.9 

October  9  5 

Ironton.  .  . 

Iron. 

April  26  4 

October  6  9 

Lebanon  .  . 

Laclede  .  .  . 
Clay  
Audrain.  .  .. 
Lawrence  .  .  . 
Newton  
Putnam  

Jefferson  
Gallatin... 

April,  14.7    . 

October,  20.7.  .  . 

.  Liberty  
Mexico  . 

April  17  5 

October  10  4 

April  16  9 

October  17  0 

Mount  Vernon.  . 
Neosho  .  .  . 

April,  23.8 

October  14  8 

April  23  7 

October  14  8 

Unionville  

April,  23.5..  . 

October  12  1. 

Montana: 
Boulder    Nurs- 
ery. 
Bozeman  

June,  12.3  

September,  3.4  

September,  7.7  
September,  16.2  
August  25  4 

May,  25  4 

Butte  

Silver  Bow.. 
Flathead  
BicHorn... 
Chouteau  .  .  . 
Dawson  
Cascade  .  .  . 
Hill  
Lewis    and 
Clark. 
Custer  

May  30  1 

Columbia  Falls  . 
Crow  Agency... 
Fort  Benton.... 
•    Glendive. 

June,  10.5 

May,  14.4.. 

September,  25.1.... 
September,  22.5  
September,  19.9  
September,  24.0.... 
September,  18.4  
September,  26.8  

September,  28.7  
September,  16.2  
September,  13.5.... 
September.  15.9... 

May,  11.7  

May  11  4 

Great  Falls  
Havre  
Helena  

May,  5.7  

May,  15.5.  .  . 

May  8  4 

Miles  City  
Missoula  
Poplar.... 

May  3  0 

Missoula  
Sheridan  
Fergus  .  .  . 

May,  24.1... 

May   13  7 

Utica  

May.'  25.8... 

ASTRONOMY,  METEOROLOGY,  AND  SEISMOLOGY. 
TABLE  2. — Frost  data  for  selected  stations — Continued. 


25 


Station. 

County. 

H. 

Years 

A.. 

<r«. 

A.. 

ff». 

Nebraska:            • 
Ashland  

Saunders 

1,120 

22 

April  23  8 

11  2 

October  10  9 

13  1 

Beatrice  

^age  

1,235 

24 

April,  25.4  

13.0 

October'  9  7 

11  6 

Beaver  C  itv  

Furnas  

2,147 

22 

May,  2  9 

11  0 

October  7  4 

11  0 

Callaway  .'... 

uster 

2  555 

21 

May  6  7 

11  1 

September  23  8 

12  0 

David  (itv  .... 

Butler  

1,619 

27 

April,  27  3 

15  6 

October  80 

14  0 

Fort  Robinson. 

Dawes  .   . 

3,764 

21 

May  11  1 

11  3 

September  19  3 

11  5 

Gothenburg  

"^"WSOn  

2,557 

21 

May,  3.8  

11.4 

September'  27  3 

11  2 

Hartington  

Cedar  

1,309 

22 

Mav,5.7  

10.0 

October,  2.8 

13  0 

Hot  Springs  .  .  . 

Sherid  n... 

3,821 

28 

May,  12.4  

8.7 

September  19  4 

10  4 

Imperial  

Chase  

3,278 

22 

May,  5.0 

11.8 

September  29  0 

11  9 

Lod"epole  

Chey«  i  le  .  . 

3,820 

19 

May,  15.6.  .  . 

9.8 

September'  19  6 

10  9 

North  Plattr... 

Linco  i.... 

2,821 

41 

May,  2.1.. 

9.9 

September  29  6 

11  0 

Dolls'  is. 

1,103 

43 

April,  15  4 

12  0 

October  12  2 

13  6 

Syracuse  

Otoe. 

1  059 

25 

April  23  6 

12  8 

October  8  3 

12  2 

Valentine  

Cherry... 

2,598 

26 

May,  6.0 

13.6 

September  30  3 

11  8 

Nevada: 
Carson  r  ty..., 

Orms'iy... 

4,720 

28 

May,  20.2.  . 

16.3 

September  21  1 

13  5 

Elko  

i-lko  . 

5.  432 

20 

May,  30  9 

16.6 

September  8  6 

15  0 

Ely... 

vv  inte  Pine 

6  421 

22 

June  10  4 

18  6 

September  11  0 

11  9 

Lewers'  Ranch 
Palmetto 

Washoe  
Esmeralda 

5,200 
6  500 

27 
20 

May,30.1  
June,  12  6 

20.5 
17  0 

September  '25.3.'.!." 
September  169 

16.8 
13  3 

Potts  

Nye.... 

6,990 

22 

June.  8.5 

21.9 

September  6  4 

20  2 

Reno.. 

Washoe 

4.500 

28 

May,  13  5 

17  1 

October  3  0 

12  2 

Wells  

KIko  

5,  623 

19 

May,  30.3.  . 

24.6 

September  173 

21  4 

Winnemucca 

Humboldt 

4  291 

36 

May,  16  6 

15.6 

September  24  6 

13  3 

New  Hampshire: 
A  Mead... 

Cheshire  .  .  . 

1,120 

22 

May,  22.1  . 

12.1 

September  26  5 

11  5 

Bethlehem  
Brookline.  .  .. 

Graft  on.... 
Hillsboro.  .  . 

1,470 

22 
22 

May,  19.3  
Mav,  17.8. 

15.9 
10.9 

September,  17.9..!! 
September  25  0 

10.9 
11  6 

Newton 

Rockingham 

126 

26 

May,  21  1 

13.7 

September  23  5 

11  7 

PI  v  month.. 

Grafton  

500 

27 

May,  22  5.  .     . 

11.0 

September'  24  6 

8  4 

New  Jersev: 
Atlantic  City  .  .  . 

Atlantic... 

16 

40 

April,  12.6..., 

9.5 

November,  2  0 

10  5 

Brideeton.  .. 

Cumberland 

30 

22 

April,  21  6 

15.3 

October  21  9 

12  2 

Charlotteburg.  . 

Passaic  

719 

22 

Mav,  10.4  

9.5 

September,  26  3 

8.8 

Somer  ille.. 

Somerset.  . 

60 

22 

May,  5.2. 

11.5 

October  8  1 

9  4 

New  Mexico: 
Agricultural 

Dona  Ana... 

3,863 

23 

April,  11.2... 

16.5 

October,  22  3 

r 

9.0 

College. 
Albuquerque... 

Bernalillo... 

5,000 

21 

April.  15.8..., 

8.1 

October,  23  3 

12.9 

Carlsbad  

Eddv... 

3,120 

19 

March.  28  8 

15.5 

October,  30  2 

9  g 

Doming  

4,  333 

22 

March,  23.1  

13.9 

October,  30.6. 

12.5 

Engle  and  Rio 

Sierra... 

4,265 

19 

April,  5.6... 

15.4^ 

October,  31  4 

12  2 

Grande  Dam. 
Fort  Union.  . 

Mora  

6,835 

20 

Mav,  15.6.  .  . 

15.2 

October,  5.6 

11.5 

Fruitland. 

San  Juan 

4,300 

20 

May,  6.7... 

12.6 

October  6  0 

9  5 

Las  Vegas  

San  Miguel.. 

6,384 

22 

Mav,  4.9  

10.0 

October,  4  9 

10.5 

Los     L  u  n  a  s 

Valencia 

4,900 

22 

April,  14.2... 

14.6 

October,  18  6 

11.8 

(near). 
Roswell 

Chares 

3  578 

21 

April.  9  0 

12  5 

October  25  9 

3-3 

San  Marcial 

Socorro 

4,454 

20 

April,  66.. 

12.8 

October  24  4 

12  6 

Santa  Fe 

Santa  Fe 

7  013 

40 

April,  24  1 

10  1 

October  19  6 

10  5 

Springer.  . 

Col  fax... 

5,857 

20 

May,  11.8.  . 

16.7 

September  30  4 

13.0 

New  York: 
Addison  

Steuben... 

1,000 

21 

Mav,  10.0.  .  . 

14.9 

October,  5  4    . 

13.8 

Angelica.. 

Allegany 

1  340 

21 

Mav,  20.8. 

17.8 

September  23  6 

14.6 

Appleton 

Niagara 

300 

26 

May,  4  0 

12  5 

October  13  6 

10  2 

Binghamton 

Broome 

875 

25 

May,  7.0.  .. 

14.1 

October,  25  0. 

11.9 

Buffalo 

Erie 

824 

24 

April,  30  6 

13.1 

October,  18  2 

11.8 

Cooperstown 

Otseeo.. 

1,  250 

24 

May,  10.0  

12.4 

September,  29.3  .  .  . 

11.9 

Glens  Falls 

Warren 

349 

21 

May,  5.9.... 

11.9 

October,  1  8 

12.7 

Glo  ersville 

Fulton 

850 

23 

May,  10  1 

12.7 

September  25  5 

9  5 

Ithaca.. 

TompMns.. 

928 

36 

May,  3.5.  .. 

13.0 

October,  10.7. 

10.3 

New  Lisbon 

Otsego 

1  234 

23 

Mav,  24  6 

12.0 

September,  22  6 

13.1 

Oswego 

Oswego 

335 

23 

April,  266 

14  5 

October  21  0 

10  1 

Oxford.. 

Chenango 

938 

24 

May,  17.3  

10.8 

September,  25.3  .  . 

12.2 

Perry  City 

Schuyler 

1  038 

25 

May,  18.2. 

13.0 

September,  26  8 

12.7 

Rochester.  . 

Monroe  .  .  . 

523 

23 

April,  23.4  

13.1 

October,  16.8  

11.7 

Romulus 

Seneca 

719 

25 

May,  6.5.  .  . 

12-9 

October,  10.4. 

12.4 

North  Carolina: 
Chapel  Hill 

Orange 

500 

30 

April,  6  5  . 

13.0 

October  28  7 

11.9 

Highlands 

Macon  .  . 

3,800 

25 

April,  25.6  

18.4 

October,  11.9  

13.5 

Lenoir 

CaldVell 

1  186 

40 

April,  165  

11.5 

October,  18  3 

10.7 

Liimberton 

R  obeson      • 

102 

20 

March,  30  9 

12  7 

November,  2  2 

11.7 

Mount  Airy 

Surrv 

1,048 

24 

April,  21.0  

13.4 

October,  16.7  

9.3 

Newbern 

Cra~>  en 

12 

24 

April,  3.5... 

13.0 

November,  5.4.  .  . 

13.5 

Salisbury 

Rowan 

760 

22 

April  105 

12.1 

October  24  6 

10  7 

South  port 

Brunswick 

18 

20 

March,  22.9  

16.3 

No"1  ember,  11.5.  .   . 

9.7 

Waynesville 

Havwood 

2  792 

21 

April,  255  

11.2 

October,  12.1  . 

11.4 

Weldon.. 

Halifax.. 

81  i 

27 

April,  12.8..., 

13.0 

October,  25.8  

9.7 

26 


PROCEEDINGS  SECOND  PAN  AMERICAN   SCIENTIFIC   CONGRESS. 


TABLE  2. — Frost  data  for  selected  stations — Continued. 


Station. 

County. 

H. 

Years.'                A.. 

«s. 

Aa. 

,.. 

North  Dakota: 
Bismarck 

Burleigh.... 
Bottineau... 
Williams-.. 
Stark  
Sargent  
McLean  
Stutsman... 
Grand  Forks 
Renville  
Billings  
Walsh  

1,674 

1,638 
1,944 
2,543 
1,249 
1,901 
1,390 
1,134 
1,640 
2,225 
820 
1,955 
2,400 
789 
1,020 
1,857 
830 
962 
1,872 
1,471 

1,276 
803 
745 
960 
975 
1,087 
627 
944 
880 
1,050 
720 
1,130 
527 
900 
588 

1,575 
1,150 
900 
1,062 
1,585 
1,247 
880 

212 
1,940 
3,471 
4,157 
100 
266 
670 
435 
220 
32 
575 
956 
1,950 
300 
1,640 
4,400 
2,784 
154 
195 

485 
69 
1,070 
510 
120 
4,700 
4,150 
112 
75 
2,242 
1,800 
1,368 

40 
20 
28 
23 
23 
20 
22 
21 
21 
18 
23 
26 
20 
32 
24 
20 
23 
22 
21 
22 

21 
22 
21 
26 
22 
21 
31 
20 
22 
27 
20 
22 
26 
21 
22 

21 
15 
21 
17 
21 
24 
21 

24 
26 
25 
20 
22 
25 
19 
21 
23 
20 
22 
22 
23 
25 
26 
22 
20 
26 
23 

22 
22 
25 
37 
22 
22 
20 
39 
24 
21 
25 
22 

May,  11.1  .  . 

10.2 
9.9 
12.4 
13.9 
17.2 
12.3 
12.0 
8.9 
12.1 
12.5 
11.5 
13.1 
10.1 
14.1 
14.6 
14.1 
13.8 
12.4 
11.8 
12.9 

14.8 
13.7 
14.9 
13.1 
9.1 
16.0 
13.1 
16.6 
12.9 
14.0 
11.7 
15.4 
12.5 
13.3 
14.5 

14.9 
15.6 
15.7 
15.4 
13.2 
15.8 
15.6 

21.7 
19.0 
21.1 
22.4 
19.0 
13.8 
25.6 
18.3 
13.0 
30.1 
22.7 
17.6 
14.2 
14.4 
12.5 
16.1 
14.7 
15.1 
18.  * 

18.9 
20.3 
19.7 
19.7 
18.4 
18.9 
22.0 
13.1 
16.1 
18.4 
18.8 
17.2 

September,  19.2.. 
September,  9.3... 
September,  23.2.. 
September,  10.3.. 
September,  20.0.. 
September,  23.  2.. 
September,  17.9.. 
September,  18.6. 
September,  5.3.. 
September,  10.9. 
September,  16.7. 
September,  9.1  .  . 
September,  9.9.. 
September,  11.1. 
September,  19.6. 
September.  12.0. 
September,  20.1  . 
September,  18.2. 
September,  21.5. 
September,  13.0. 

October,  8.2 

11.1 
19.1 
1018 
17.7 
17.3 
12.4 
12.4 
13.7 
14.6 
13.5 
10.3 
12.2 
8.8 
12.0 
12.8 
12.1 
12.8 
14.1 
13.8 
8.6 

11.7 
12.5 
10.8 
12.2 
13.0 
11.4 
10.6 
12.2 
13.0 
9.8 
14.7 
11.3 
13.2 
11.4 
14.0 

9.7 
8.8 
8.8 
13.4 
9.6 
11.0 
12.8 

20.3 
18.0 
13.2 
19.0 
16.1 
16.8 
14.6 
21.2 
19.1 
19.9 
20.2 
15.9 
16.8 
18.7 
17.0 
18.2 
18.6 
21.9 
20.0 

23.0 
19.6 
15.6 
19.9 
20.6 
11.0 
16.1 
12.5 
17.0 
13.6 
16.5 

17.  a 

Bottineau 

May  199 

Buford 

May,  12.3       

Dickinson  
Forman  

May,  24  8 

May,22.3  

Garrison  
Jamestown  
Larimore    .  .  .  . 

May  18  3 

May,23.0  

Mo  TTir|  fifty 

May  28.2 

Medora  

May,  20.0  

Minto  

May  26.7 

Napoleon 

Logan 

May  27  1 

New  England.. 
Pembina 

Hettinger... 
Pembina  
Richland... 
Kidder  . 

May,  19.0  - 

May,26.2  
May,24.5  

Power  

Steele.   ..  . 

Mav,  23.0 

University  
Wahpeton  

Grand  Forks 
Richland... 
Williams.... 
Bottineau... 

Logan  . 

May,  18  2 

May,  18.0  

Williston 

May,16.2  
May,  16.9  

t'«g   G    1 

Mav  1  2 

Willow  City.... 
Ohio: 
Bellefontaine.  .. 
Cambridge  

Guernsey.  .  . 
Ross 

May,  8.2  

October,  2.0  

Frankfort  .  .  . 

April  28.0 

October,  12.0 

Granville...  

Licking  
Butler  

April,  30.0  

October,  8.3  

Jacksonboro  
Killbuck 

April,  28.6     .  .  . 

October,  17.2 

Holmes  
Washington. 
Medina 

May  4  8 

October,  5  4 

Marietta  

April,  18.7  

October,  21.9 

Medina 

May,  13  3 

October  9  2 

Montpelier  

Williams.... 
Jefferson  
Putnam  
Clark  

May,  2.0  

October,  6.5  

New  Alexandria 
Ottawa 

April,  30.5         . 

October,  11.2  . 

May  3  8 

October  7  0 

Plattsburg  

May,  2.2  

October,  5.9  

Portsmouth  
Warren 

Scioto 

April  16  8 

October  21.0 

Trumbull... 
Sandusky... 

Ouster 

May  14  3 

October  5  7 

Vickery  

May,  8.1 

October,  9.5 

Oklahoma: 
Arapaho 

April  7  6 

October  28  5 

Fort  Sill  

Comanche... 
Carter 

March,  28  2 

November  7.4 

Healdton 

April  4  3 

October  29  7 

Jefferson  

Grant  

April,  12.6  
March  24  3 

October,  24.5 

Mangum  
Oklahoma  

Greer  
Oklahoma.. 
Payne 

November  3  6 

April,  1.5  

Nov.  1.0  

Stillwater.  . 

March,  30.3  
March,  31.0     ... 

October  29  5 

Oregon: 
Albany  
Ashland  
Baker  
Burns  

Linn  
Jackson  
Baker  
Harney  
Hood  River. 
Benton 

October,  30.5      

April  16  8 

October  21  3 

Mav,  16.0  

September,  26.0..  . 
September,  16.2..  . 
November,  11.9..   . 
October  16  5 

May  286 

Cascade  . 

April  8  4 

Corvallis 

April,23.5  
March  14  7 

Eola  

Polk 

November,  10.4.  .   . 
November,  2.3...  . 
October  16  5 

Eugene  
Forest  Grove... 
Gardiner  

Lane  
Washington. 
Douglas  
Tillamook... 
Josephine.  .. 
Morrow  
Hood  River. 
Jackson  
Wallowa.... 
Union  .... 

April  9  1 

April  30  7 

March  26  4 

November,  29.5  
October,  2.8 

G  lenora  

May,  19.1         .    . 

Grants  Pass  
Heppner  . 

May  15  2 

October  1  5 

April  29  3 

October  12  9 

Hood  River  
Jacksonville  
Joseph  . 

April  15  8 

October,  22.7    . 

April,  17.3  
Mav  12  0 

October,  29.7  

October  5  5 

»      La  Grande... 

Apri'1,22.9  
April,  28.3  

October^  4 

McMinnville.... 
Miramon  te 
Farm. 
Mount  Angel... 
Newport  
Pendleton  

Yamhill  
Clackamas.. 

Marion 

October,  11.7  

April,  23  1     . 

October,  31.7 

April  1  7 

November,  3.5  
November,  29.8  
October  2  2 

Lincoln  
Umatilla.... 
Douglas  
Marion 

March,  24.7  

May  5  8 

Roseburg. 

Apr.ii  14  8 

November,  12.1  

Salem 

April  7  0 

Silver  Lake  

Lake. 

June  17  0 

September',  1.9  
October,  14.6  
October  23  3 

Sparta  

Baker 

May,3.4  

Tlie  Dalles  
Toledo  
Vale  
Weston  
Williams  

>.II 

Wasco  
Lincoln  
Malheur.  .  .. 
Umatilla.... 
Josephine... 

April'  19.5  
May,20.1  

November  4.2  
September,  11.7  
October  6  1 

May'  10.4  

September,  24.2  

1^,8  i! 

ASTRONOMY,  METEOROLOGY,  AND  SEiSMOLOGY.>oafjt 

TABLE  2. — Frost  data  for  selected  stations — Continued. 


27 


^,    |  Station.  ^A 

County. 

H. 

Years. 

As. 

at. 

Aa. 

<Ta. 

Pennsylvania: 
Coatesville  

Chester  

380 
1,050 
650 
1,148 
458 
450 
580 
634 
528 
1,116 
754 
999 
1.327 
455 

250 
182 

85 

12 
711 
192 
875 
620 

1,300 
1,352 
1,636 
1,248 
1,789 
1,726 
1,595 
1,565 
1,231 

21 
21 
21 
20 
20 
21 
21 
21 
20 
21 
20 
20 
32 
31 

25 
30 

22 

22 
22 
23 
20 
22 

25 
25 
27 
20 
19 
20 
21 
24 
24 
20 
23 
24 
34 
27 
24 
22 
21 
24 
23 
27 
21 
24 
25 
20 
22 
22 
24 
22 

23 
23 
23 
44 
43 
23 
22 
21 

29 
23 
20 
24 
13 
16 
25 
24 
31 
22 
23 
20 
27 

April,  20.1... 
May  13  8 

9.5 
11.9 
16.0 
15.0 
14.0 
15.1 
14.0 
12.9 
14.1 
15.2 
11.4 
15.4 
18.6 
10.2 

9.0 
9.1 

14.4 

15.6 
12.6 
12.8 
10.9 
13.1 

12.5 
13.2 
13.4 
15.5 
15.4 
13.3 
11.9 
14.5 
13.9 
10.6 
10.8 
13.7 
13.1 
10.1 
12.7 
14.9 
11.5 
8.7 
8.3 
9.7 
11.5 
10.3 
15.5 
15.0 
10.5 
13.5 
17.0 
11.2 

10,6 
8.7 
10.6 
10.7 
14.3 
10.4 
11.4 
13.0 

13.9 
13.2 
15.2 
18.5 
18.6 
15.3 
16.1 
15.9 
18.6 
18.6 
15.2 
13.6 
15.6 

October  159 

10.2 
11.8 
12.9 
10.7 
10.1 
8.9 
11.5 
9.7 
10.4 
10.9 
11.8 
10.1 
11.3 
10.2 

11.9 
13.5 

11.6 

12.3 
11.0 
10.9 
11.8 
14.9 

13.6 
14.3 
13.1 
12.9 
11.7 
12.6 
11.1 
11.6 
12.7 
11.7 
11.8 
14.6 
12.7 
10.5 
11.1 
14.0 
12.2 
14.5 
13.1 
10.5 
12.9 
13.2 
12.0 
17.0 
13.2 
10.3 
11.4 
13.0 

9.5 

10.5 
12.6 
12.7 
12.8 
10.4 
12.1 
10.0 

12.4 
10.3 
13.7 
11.2 
11.7 
14.1 
11.1 
11.0 
14.0 
12.6 
9.9 
7.7 
12.  fr 

Emporium  
Huntingdon  
Johnstown  

Cameron  
Huntingdon. 
Cambria  
Lebanon 

October  5  5 

May,  7.3  

October'  6  6 

May.  2  6 

October  11  7 

Lebanon  .   . 

April  27  8    . 

October  11  6 

Lewis  burg  
Lock  Haven  
Mauch  Chunk.. 
Quakertown  
Saegerstown  
Towanda  

Tnion  

May,  44  .. 

October'  12  3 

Clinton  .  . 

April.  30  8. 

October  11  7 

Carbon  

April,  30.4.... 

October  9  6 

Bucks  

April,  29  8... 

October  8  2 

Crawford  
Bradford.... 
,  Fa5^ette. 

May  21  0 

September,  26.  i  
October  4  9 

May,  3.9  

Uniontown  .  . 

April,  26  4.  . 

October  187 

Wellsboro  
West  Chester... 
Rhode  Island: 
Kingston  

Tioga  
Chester  

May,  16.1  

September,  25.9"... 
October  23  4 

April,  15  1... 

Washington*. 
Providence.  . 

Berkeley  

Georgetown. 
Newberry.  .  . 
Darlington.. 
Spartanburg 
Edgefield... 

Brown. 

April,  28.2.  . 

October  13  1 

Providence  
South  Carolina: 
Ferguson    & 
Trial. 
Georgetown  
Little  Mountain 
Society  Hill.... 
Spartanburg  
Trenton 

April,  21  6... 

October  17  1 

March,  253... 

November  5  8 

March  10  4 

November,  20.1  
November,  11.0  
November,  9  0 

March,  24  9... 

March,  19.7  
March,  302... 

November  1  8 

March  18  5 

November,  15.6  

September,  20.1  
September,  26.3  
September,  21.1  
October  1  3 

South  Dakota: 

May,  19  0 

Alexandria  
Brookings  

Hanson  
Brookings... 
Lincoln 

May  13  1 

May,  18  8  .  . 

Canton 

May  88 

Clark  

Clark  

May,  18.7  

September,  25.5..  . 
September,  21.8..  . 
September,  26.2..  . 
September,  21.5..  . 
September,  22.1  .  .  . 
October  3  5 

De  Smet... 

Kingsbury.. 
Faulk....... 
Moody. 

May  12  7  . 

Faulkton  
Flandreau*. 

May,  11.2  

May,  14  9  .  . 

Forest  burg  
Greenwood  
Highmore 

Sanborn  
Charles  Mix. 
Hyde 

May  15  0 

April,  298... 

1,890 
1,564 
1,306 
1,788 
1,148 
1,300 
1,312 
3,339 
1,572 
3,234 
2,600 
1,400 
3,647 
1,418 
1,222 
1,735 

May  129 

September,  28.6  
September,  18.1  
September,  21.9  
October,  1  5 

Howard  

Miner  

May,  15  7  .  . 

Huron.. 

Beadle. 

May  11  5  . 

Kimball  
Milbank.. 

Brule  
Grant... 

May,  6.0  

May  131... 

September,  27.2... 
September,  22.5  
October,  1  2 

Mellette 

Spink 

May  177 

Mitchell  

Davison  .  . 

May,  1JO  

Oelrichs 

Fall  River.. 
Hughes  
Pennington. 
Todd  
Minnehaha.. 
Lawrence... 
Bonhomme. 
Clay  
Codington.. 
Lake. 

May  13  5 

September,  18.3  
October  6  2 

Pierre 

April  30  6 

Rapid  City  
Rosebud  
Sioux  Falls  
Spearfish 

May,  5  3 

September,  27.8  
September,  26.4  
September,  27.1  
September,  28.9.... 
September,  26.4  
October  6  1 

May  11  5 

May,  94  

May  73 

Tyndall  

May,  7.9  

Vermilion  
Watertown  
Went  worth.. 

May,  40.. 

May  226 

September,  20.4  
September,  26.  4  
October  5  5 

May,  18.  2     . 

Yankton 

Yankton.... 

Montgomery 
Rutherford.. 
Lewis 

1,233 

500 
560 
983 
1,028 
347 
1,150 
1  410 
442 

1,738 
3,676 
1,637 
1,342 
1,869 
2,066 
445 
3,762 
1,050 
3,050 
738 
1,553 
400 

May  26 

Tennessee: 
Clarksville  
Florence 

April,  47... 

October,  25  0 

April  4  4 

October  23  7 

Hohenwald.. 

April,  13.3... 

October,  13  1 

Knoxville 

Knox; 

April  2  7  . 

October  26  4 

Memphis 

Shelby  ' 

March,  21.9  

November,  1.6.  .. 

Rogersyille  
Rugbv 

Hawkins.  .  .  . 
Morgan 

April,  165... 

October,  18  8 

April  22  8 

October  12  5 

Savannah 

Hardin... 

April,  26... 

October,  24.6 

Texas: 
Abilene 

Taylor 

March  21  5 

November,  10.0  
October,  28  5 

Amarillo 

Potter 

April.  166  

Ballinger 

Runnels  

March  272... 

November  6  4 

Brown  wood  
Childress 

March  24  8 

November  7  6 

Childress.  .  .  . 
Mitchell  
Navarro  
El  Paso  
Kinney  
Pecos  
Cooke... 

April,  39...     . 

November,  6.4  
November,  6.6  
November,  13.1  
November,  16.9  
November,  25.4  
November,  6.9  
November,  6.5  
November,  11.6  
November.  22.3  

Colorado 

April  5  4... 

Corsicana  
El  Paso 

March  15  8    . 

March,  10.6  

Fort  Clark  
Fort  Stockton.. 
Gainesville  
HasVell.. 

February,  26.8  
March  30  6 

March,  26.7  
March,  29.4  

Haskell  
Walker... 

Huntsville... 

March.  6.6.... 

28  PROCEEDINGS   SECOND  PAN   AMERICAN   SCIENTIFIC   CONGRESS. 

TABLE  2. — Frost  data  for  selected  stations — Continued. 


Station. 

County. 

H. 

Years. 

AB. 

ff«. 

1            A.. 

««• 

Texas—  Continued. 
Llano 

Llano 

1,040 

23 

March,  192... 

21.2 

November,  17  7 

10  6 

Gregg 

336 

24 

March  124 

12.7 

November  16  5 

10  6 

Mount  Blanco 

Crosby 

2,750 

20 

April.  7.2  

14.2 

October,  296.  ' 

8.7 

New  Braunfels 

Comal... 

720 

26 

March  40... 

11.8 

November  25  8 

12  7 

Paris 

Lamar 

592 

24 

March  189 

18.1 

November  11  8 

8.7 

Temple  . 

Bell. 

630 

24 

March,  10.2... 

14.7 

November,  17  9 

12  3 

Weatherford 

Parker 

864 

24 

March  23  7... 

19.5 

November  10  6 

8  8 

HQtah: 
Connne  .. 

Boxelder. 

4,240 

20 

May,  16.6 

15.1 

September  28  8 

14.4 

Deseret 

Millard 

4,541 

20 

May  280 

14  8 

September  14  3 

11  2 

Fillmore.. 

..  ..do     .. 

5.100 

23 

Mav,  22.4 

19.0 

September,  22.1 

12.5 

Heber 

Wasatch 

5,593 

25 

June  20  6 

14.0 

August  30.7 

9  s 

Levan 

Juab... 

5.010 

20 

Mav,  29.6  

16.0 

September,  29.4 

13.8 

Loa 

Wavne    .. 

7.000 

18 

June,  19.7 

14.9 

September,  4  6 

12  2 

Logan 

Cache 

4,507 

23 

May  14  :-! 

16.6 

October  5  1 

15  1 

Manti 

Sanpete    .  . 

5.575 

20 

Mav,  24.2  . 

19.1 

September,  21.4 

14.5 

Moab 

Grand 

4,000 

25 

April   19.4 

12.3 

October,  5  8 

14  0 

Parowan  

Iron  

5.970 

24 

May,  29.5  

13.0 

September,  25.9. 

10.3 

EichPeld 

Sevier 

5.350 

19 

June.  2.6 

15.8 

September,  18.1 

1?  7 

St  George 

Washington 

2,880 

25 

April  21  S 

17  9 

October  10  3 

16  1 

Salt  Lake  City.. 

Salt  La:  e.. 

4.360 

40 

April,  20.9..     . 

18.0 

October.  19.2     . 

13.4 

Scipio 

Millard    . 

5,260 

20 

June,  17.6 

14  9 

September  7.2 

9  7 

Vernal  

Uinta  

5,060 

17 

Mav,  16.2  

16.  P 

September,  25.2     . 

11.2 

"Vermont: 
Enosburg  Falls. 

Fran"  lin  

601 

24 

May.  15.9... 

12.3 

September,  18.5  

8.0 

Jac  sonvalle  

Windham... 

1.000 

25 

Mav,  22.6  ... 

12.0 

September,  15.1 

12  6 

Northfield... 
Wells  

Washington. 
Rutland  .  .  . 

876 
750 

28 
23 

Mav,  22.6  .  .  . 
May,  9.5  

11.2 
12.  5 

September.  16.4  
October,  1.8  

13.2 
11.6 

Woodstock 

Windsor      . 

700 

34 

May,  13.8 

16.3 

September.  27  2 

11.3 

Virginia: 
Big  Stone  Gap.. 

Wise  

1.540 

22 

April,  24.4... 

12.1 

October,  14.5      .     . 

11.2 

Birdsnestw 

Northamp- 

40 

28 

March,  29.8 

11  5 

November,  18  9 

9.9 

BlacJ'sburg 

ton. 
Montgomery 

2,170 

23 

April,  28.6... 

15.4 

October,  7.6 

14.3 

Dale  Enterprise 

Rocking  - 

1.450 

46 

April,  27  7 

12  9 

October  9  2 

12  4 

Fort  Monroe 

ham. 
Elizabeth 

8 

28 

March,  21.0    . 

16.0 

November  24.3 

14.9 

Frederic"  sburg 

City. 
Spotsylvania 

100 

22 

April,  10.9  . 

13.1 

October,  23.7 

10  5 

Hot  Springs 

Bath 

2  195 

23 

May,  1.0 

13  1 

October  8  0 

10  9 

L  \nchburg.  .  . 

Campbell  .'  . 

681 

42 

\pril,  8.1.  .. 

13.2 

October,  27.4. 

12.8 

Marion 

Smvthe 

2,  135 

29 

\pnl,  22.9 

11  5 

October  11  0 

11.1 

Norfolk  

Norfolk  •.     . 

01 

42 

March  24.  6... 

13.8 

November  16.5  

12.0 

Petersburg  . 

Dimviddie 

60 

28 

April,  9.7.  . 

13.2 

October  25.4 

12.3 

Sta.uTit.on 

Augusta 

1  380 

25 

April  189 

10  2 

October  15  7 

10  2 

Warsaw  

Richmond 

200 

22 

April,  13.1 

11.3 

October,  24.4 

9.6 

Washington: 
Aberdeen  

Chehalis  

162 

24 

Apnl,  20.8.... 

17.5 

October,  27.2  

22.1 

Bellingham... 

Whatcom 

60 

20 

April,  22.0 

19.  -» 

October  19.1 

19.0 

Centralia 

Lewis 

212 

19 

May  6  1 

1C  6 

October  13  8 

20  3 

Colfax  

Whitman 

2.300 

21 

Mav,  22.8 

17.0 

September,  16.1 

14.9 

Ellensburg 

Kittitas 

1.571 

23 

May,  13.0 

13  3 

September  21  6 

11.0 

La  eside  

Chelan  

1.116 

21 

April,  9.6  

13.4 

October,  20.8 

12.8 

Moxee  .  .  . 

Yakimp,. 

1  000 

23 

Mav,  17.2 

16.1 

September  21.0 

11.7 

Olga    .. 

San  Juan 

50 

03 

April  8  1 

22  1 

^ovember  9  5 

2-4  7 

Olympia  

Thurston  .  . 

45 

37 

April,  21.4... 

19.7 

October,  27.5 

22.4 

Pomeroy  .  . 

Garfield 

1,860 

21 

April,  26.0 

17  7 

October  5  0 

25.5 

Port  Crescent... 

Clallam  .  .  . 

259 

16 

April,  3.5  

16.8 

October,  29.5  

13.9 

Pullman 

Whitman 

2  550 

21 

Mav  7  7 

16  5 

October  4  1 

14  9 

Resalia  . 

...do  . 

2  425 

22 

May,  27  1 

26  5 

September  23  2 

17.7 

Seattle  

King  

248 

24 

March,  20.1.. 

21.1 

"ovember,  22.6.  . 

15.4 

Snohomish  

Snohomish 

55 

20 

April,  22.5 

22.5 

October  20.4 

25.1 

Spo"  ane  

Spo'  ane.  .. 

1,943 

33 

April.  11.4..... 

21.0 

October,  12.5  

17.3 

Sunnyside  

Yakima. 

740 

20 

May  3.3 

16.2 

October,  5.8 

12.6 

Walla  Walla.. 

WallaWalla. 

1,000 

29 

March,  30.0... 

15.9 

November,  7.7  

16.0 

Waterville  

Douglas  .... 

2,624 

22 

Mav,  24.9  . 

16.1 

September,  20.8 

16.3 

West  Virginia: 
Buekhannon  

TTpshur 

1  411 

21 

May,  7  4 

15  9 

October  3  7 

8.9 

Burlington  

Mineral  

875 

21 

May,  7.6  . 

15.9 

October,  3.8 

11.0 

Elkhorn... 

McDowell. 

1,933 

23 

April,  24  .9 

11.5 

October,  12.5 

11.6 

Glenn  ville  

Gilmer  

738 

24 

April,  29.1  

11.6 

October,  12.5  

11.0 

Grafton  

Taylor  

1,000 

23 

Mav,  3.9 

11.0 

October,  9.0  

10.9 

Martinsburg  

Berkeley 

435 

24 

April,  19  1 

11  2 

October,  17.2 

10.1 

Nuttallburg  

Favette... 

2,252 

20 

Mav,  3.6.   . 

14.4 

October,  11.1  

10.7 

New    Martins- 

Wet/el  

634 

23 

April,  27.7 

14.2 

October,  15.8        .  . 

9.4 

vllle. 
Point  Pleasant.. 

Mason... 

553 

23 

April,  22.0.... 

13.7 

October,  15.9... 

10.6 

ASTRONOMY,   METEOROLOGY,  AND   SEISMOLOGY. 


29 


TABLE  2. — Frost  data  for  selected  stations — Continued. 


Station. 

County. 

H. 

Years. 

A.. 

«s. 

Aa. 

*». 

Wisconsin: 
Florence    

Florence  

1.293 

21 

May, 

29.4  .  .  . 

8.8 

September,  16.3 

12  3 

Gi'iinlsburg 

Burnett  

1  095 

22 

May, 

20.1.  . 

14.9 

September  20  9 

9  0 

Green  Bay  

Brown  

5X6 

2* 

Mav, 

5.5  

11.4 

October,  9.2 

12.3 

La  Grouse.. 

La  Crosse  

681 

42 

Aori 

,26.1  

14.4 

October,  11.9 

9  8 

Madison 

Dane 

•97'r 

37 

Apn 

2'>  <* 

9  7 

October  17  3 

10  7 

Manitowob  

Manitowoc.. 

616 

31 

Mav, 

1.6...*  

11.2 

October,  K-i.R 

10  9 

Glnrk 

°96 

22 

Mav 

17  5 

13  2 

September  24  2 

12  5 

PrairiPdu  rhien 

Cra  \v  ford 

628 

24 

\pri 

,  27  2 

13  1 

October  1  1  6 

11  6 

Valley  Junction. 
Wyoming: 
Chevenne  
Fort  Larauiie  .. 

Monroe  

Laramie.  .  .. 
Gosben  

/    930 

6.  OSS 
4,472 

22 

42 
20 

May, 

Mav. 
Mav, 

13.9  

20.3  .  .  . 
16.0  

14.1 

10.0 
11.1 

September,  19.5  

September,  17.2.     . 
September,  18.4 

17.8 

11.3 
11  2 

Laramie 

Albany 

7  188 

24 

MaV, 

30.2 

16.1 

September  10  8 

10  8 

Lander  

Fremont  

5,367 

21 

Mav, 

2?  .5  

16.1 

September,  11.0 

11.9 

Lusk 

iobrara 

5.007 

22 

Mav, 

24.1.. 

15.2 

September  14  7 

28  6 

Sheridan 

Sheridan 

4  000 

19 

Mav, 

189 

8  4 

September  17  0 

7  7 

Yellow  stone 

6,200 

13 

Mav, 

24.1..  . 

15.8 

September,  13.8 

17  1 

Par;. 

Explanation  of  symbols: 

H  is  elevation  above  sea  level. 

As  is  the  arithmetical  average  of  the  dates  of  the  last  Hlling  frost  in  each  year  of  record. 

*»  is  the  stin  larl  deviation  of  the  date  of  last    illing  frost  in  spring. 

Aa  is  the  arithmetical  average  of  the  dates  of  the  first  ]  illing  frost  in  each  year  of  record. 

*  a  is  the  standard  deviation  of  the  date  of  first  Jailing  frost  in  fall. 

TABLE  3. — Factors  for  determining  the  chance  of  killing  frost. 


Killing  frost  will  occur  on  the  average  in— 

In  spring  after. 

In  fall  before. 

1  year  in  2 

As 

A8+0.  431  *s 
A8+  .674*8 
A8+  .842<78 
A8+1.282*g 
A8+1.50l*8 
A8+1.645*8 
A8+  1.751*8 
A8+1.834*8 
A8+2.054*8 
-A»+2.326*8 

•  Aa-0.  431  *. 
Aa—  .  674  * 
Aa-  .842* 
Aa-  .282* 
Aa-  .501* 
Aa-  .645* 

Aa-    '884* 

Aa-2.054* 
A  a-  2.  326* 
Aa-3.090* 

1  year  in  b.  

1  year  in  4 

1  year  in  5 

1  year  in  10  .. 

year  in  15 

year  in  20... 

vear  in  25  .  . 

year  in  30 

year  in  50  .. 

year  in  100.. 

1  year  in  1,000 

Aa+3.  090  <rs 

When   As   is  the  average  date  of  last  killing  frost  in   spring  and  An   is  the  average 
date  of  first  killing  frost  in  fall  and  ffft  is  the  standard  deviation  of  the  last  killing  frost 
in  spring  and  ffa  the  standard  deviation  of  the  first  killing  frost  in  fall.1 

To  determine  the  lengflfr^f  time  after  (or  before)  the  average  date  when 
the  last  (or  first)  frost  JpPlikely  to  occur  in  a  given  number  of  years  it  is 
necessary  to  multiply  the  standard  deviation  by  a  given  factor  as  shown  by. 
Table  3.  For  example,  if  the  standard  deviation  is  multiplied  by  1.2S  and  the 
product  added  to  the  average  date  of  last  killing  frost  in  spring,  a  date  is 
obtained  after  which  the  last  killing  frost  in  spring  will  occur  on  the  average 
]  year  out  of  every  10;  or  for  fall,  before  which  the  first  killing  frost  will 
occur  in  1  year  in  10  when  the  product  of  1.28  times  the  standard  deviation 
is  subtracted  from  the  average  date.  An  example  of  the  method  by  which 
these  dates  are  obtained  is  shown  in  Table  4,.  which  is  the  record  for  Bismarck, 
N.  Dak.  Other  factors  as  shown  in  Table  3  are  used  for  other  probabilities. 
A  curve  prepared  by  W.  J.  Spillman  makes  it  possible  to  determine  similar 
relations  for  any  number  of  years  for  from  1  in  2  to  1  in  200.2 

1  When  some  years  are  frost  free,  the  date  after  (or  before)  which  there  is  less  thnn 
one  chance  of  frost  in  two  (or  any  other  number)  may  be  determined  from  the  Spillman 
curve.  See  Spillman,  W.  J.,  Tolley,  H.  R.,  and  Reed,  W.  G.  :  The  average  interval  curve 
and  its  application  to  meteorological  phenomena,  U.  S.  Monthly  Weather  Review,  44  :  197- 
200,  Washington,  1916. 

8  Spillman,  W.  J.,  Tolley,  H.  R.,  and  Reed,  W.  G. :  The  average  interval  curve  and  its 
application  to  meteorological  phenomena.  [U.  S.]  Monthly  Weather  Review,  44:  197-200,. 
Washington,  1916. 


30 


PROCEEDINGS  SECOND  PAN  AMERICAN   SCIENTIFIC   CONGRESS. 


TABLE   4. — Frost   data   and   computations    of   frost    probability   for   Bismarck 
(Burleigh  County),  N.  Dak. 


Year. 


1875. 
1876. 
1877. 
1878. 
1879. 
1880. 
1881- 
1882. 
1883. 
1884. 
1885. 
1886. 
1887. 
1888. 


May  3 
May  5 
May  3 
May  15 
May  6 
Apr.  29 
May  2 
May  23 
May  11 
May  1 
May  9 
May  2 
May  17 
June  6 
May  H 
May  15 
May  5 
May  4 
May  27 
May  3 
May  21 
Apr.  24 
May  31 
May  4 
May  13 
May  4 
June  7 

1902 Apr.  29 

1903 i  May     5 

1904 :  May  14 

1905 May   12 

1906 j  May   27 


1891. 
1892. 
1893. 
1894. 
1895. 
18%. 


1900. 
1901. 


Last  killing  frost  in 
spring. 


Date.        d. 


1907 
1908 


May 

May 


1909 May  13 

1910 1  May  17 

1911 i  May  3 

1912 !  May  13 


1913. 
1914. 


40  years. 


May 
May 


13 


May  12 


-  7 

g 

+  3 

-  6 
-13 
-10 
+  11 

-  1 
-11 

-  3 
-10 
+  5 
+25 
+  2 
+  3 

-  7 

-  8 
+15 

-  9 
+  9 
-18 
+19 

-  8 
+  1 

-  8 
+  26 
-13 

-  7 
+  2 

0 

+15 
+  2 
-10 
+  1 
+  5 
—  9 
+  1 

-  6 
+  1 


d*. 


81 

49 

81 

9 

36 

169 

100 

121 

121 
9 

100 

25 

625 

4 

9 

49 

64 

225 

81 

81 

324 

361 

64 

1 

64 

676 

169 

49 

4 

0 

225 
4 

100 
1 

25 

81 

1 

36 
1 

4,226 


First  killing  frost  in 
fall. 


Date. 


Sept.  19 
Sept.  20 
Sept.  20 
Sept.  10 
Sept.  18 
Sept.  13 
Sept.  15 
Sept.  23 
Sept.  8 
Sept.  27 
Oct.  3 
Sept.  18 
Sept.  15 
Sept.  12 
Sept.  26 
Sept.  13 
Aug.  23 
Sept.  13 
Sept.  16 
Sept.  17 
Aug.  31 
Sept.  10 
Sept.  16 
Sept.  9 
Sept.  19 
Sept.  26 
Sept.  18 
Sept.  12 
Sept.  14 
Sept.  11 
Oct.  11 
Oct.  9 
Sept.  27 
Sept.  27 
Sept.  24 
Sept.  9 
Oct.  20 
Sept.  25 
Sept.  21 
Oct.  14 

Sept.  19 


0 

+  1 
+  1 

-  9 

=  i 

+  4 
-11 
+  8 
+  14 

-  1 
—  4 

-  7 
+  7 

-  6 
-27 

-  6 

-  3 

-  2 
-19 

-  9 

-  3 
-10 

0 
+  7 

-  1 

-  7 
5 

-  8 
+22 
+20 
+  8 
+  8 
+  5 
-10 
+31 
+  6 
+  2 
+25 

+10 


0 

1 

1 

81 

36 
16 
16 

121 
64 

1% 
1 

16 
49 
49 
36 

729 


4 

361 

81 

9 

100 

0 

49 

1 

49 

25 

64 

484 

400 

64 

64 

25 

100 

961 

36 

4 

625 

4,964 


Spring. 


Definition  of  symbols. 


Pall. 


n=40 

3f»=May  12.. 


2«f=-36... 


a=10.2. 


Ct=  May  24.2.. 


1.5 


n  is  the  number  of  observations  (years  of  record) 

M»  is  the  average  calender  date  of  last  killing  frost  in  spring* 

Ma  is  the  average  calendar  date  of  first  killing  frost  in  fall* 

d  is  the  departure  from  M. 

2d  is  the  algebraic  sum  of  column  d 

2d»  is  the  algebraic  sum  of  column  d* 

A  is  the  theoretical  average  date  A  =-  M+^ ........ 


a  is  the  standard  deviation.  /:= 

EA  is  the  probable  error  of  the  average  date.    EA=*  ±0.674 


n=40. 
Jfo=Sept.l9. 

2d=+10. 
Zd*=4964. 

^L  a*-  Sept.  19.2. 


-  ±1.2. 


Eff  is  the  probable  error  of  the  standard  deviation.    £>=  ±0.674-^=  ..... 
Ci  is  the  date  after  which  killing  frost  will  occur  in  1  year  in  on  the  aver- 


Co, is  the  date  before  which  killing  frost  will  occur  in  1  year  in  10  on  the 
average  Ca=  A  a  —  1  .28  ffa. 


_ 

EC  is  the  probable  error  of  C.    Ee=  JEAZ+(1.28  J£«0« 
Nt  is  the  calendar  date  after  which  killing  frost  will  occur  1  year  in  10* 
No.  is  the  calendar  date  before  whichikilling  frost  will  occur  1  year  in  10*. 


Ca=  Sept.  5.0. 

Ec=  ±1.6 
Jfc-Sept.5. 


*  The  calendar  date  M»  is  determined  from  A  «  by  increasing  the  date  one  whole  day  whenever  A » contains 
a  fraction,  no  matter  how  small.  A~«  is  determined  in  a  similar  manner  from  Ct. 

Ma  is  de  ermined  from  Aa  by  dropping  any  fraction,  no  matter  how  large.  No,  is  similarly  determined 
from  Co. 


oa*i       o 

ASTRONOMY,  METEOROLOGY,  AND  SEISMOLOGY.  3 


For  any  place  in  the  United  States,  then,  which  has  a  record  covering  a 
period  of  approximately  20  years,  it  is  possible  to  determine  with  very  con- 
siderable accuracy  the  risk  of  a  killing  frost  after  any  particular  date  in 
spring  or  before  any  particular  date  in  fall. 


FIG.  7.—  Dates  of  last  killing  frost  in  spring,  1907,  in  Kansas. 


1391  9ftt 

,o  9flo 


AVERAGE   DATES    OF   LAST   KILLING  FROST   IN    SPRING. 

In  order  that  a  proper  study  may  be  made  of  the  regional  distribution  of 
frost  condition,  it  is  desirable  to  map  as  far  as  possible  the  conditions  of 


U5         IQO          95  9O  85  BO  75  70  65 


115°          no1 


FIG.  8.-Average  dates  of  last  killing  frost  in  spring. 
t\' )!;'•>  '   '+i!J  rtfloHq'-nX'J  lonhil  ^197 

frost  occurrence.  Figures  8  to  13  show  the  frost  conditions  as  far  as  is  prac- 
ticable on  small-scale  maps  with  the  data  available.  Figure  8  is  a  map  of  the 
average  date  of  last  killing  frost  in  spring  for  the  United  States  based  on 


32 


PROCEEDINGS   SECOND   PAN   AMERICAN   SCIENTIFIC   CONGRESS. 


the  period  1895-1914.  In  the  eastern  United  States  isochronal  lines  have  bcon 
drawn  for  the  1st,  llth,  and  21st  of  each  month  from  March  1  to  June  1. 
In  addition,  lines  showing  the  limit  of  annual  frost — that  is,  the  line  separating 


125  12O  115  HO  105         1OO  95  90  85  8O  75  70  65 


9O°  8l>  8O°  75° 


FIG.  9.— A  erage  date  of  first  killiag  frost  in  fall. 

the  regions  where  frost  occurs  at  least  once  in  each  year  from  those  in  which 
one  or  more  winters  passed  with  no  record  of  killing  frost,  and  the  line  mark- 
ing the  regions  which  have  more  than  half  the  winters  without  killing  frost — 


125  12O  115  11O  1O5        KXr 


90  85  8O  75 


115° 11O* 1O 


85°  80'  75° 


FIG.  10.— Average  length  of  the  season  (number  of  days)  without  killing  fiost. 

have  been  entered  on  the  map.  This  map  shows,  in  the  first  place,  that  with 
very  minor  exceptions  the  whole  United  States  is  subject  to  killing  frost  each 
year.  It  also  shows  clearly  the  large  area  of  the  United  States  which  is 


ASTKONOMY,   METEOROLOGY,  AND   SEISMOLOGY. 


33 


subject  to  frost  after  June  1.     It  should  be  noted  that  the  isochronal   lines 
on  these  maps  represent  the  dates  which  will  be  exceeded  on  the  average  in 


125  I2O°  115  HO  IO5°       1OO°          95"  r>G"  if 


!i-";°  i!O  '05°  100°  95*  SO'  85 


FIG.  11.— Computed  dates  when  the  chance  of  killing  irost  falls  to  1  in  10.    After  these  dates 
killing  frost  will  occur  only  10  years  in  a  century. 

one  year  out  of  two,  that  is,  along  the  line  marked  June  1  one  year  out  of 
every  two  on  the  average  will  have  a  killing  frost  after  June  1.     A  striking 


125 12O  115  11O  IO3         1OO'         95  9O  85  8O        .     75  70*  65" 


us0          no" 


105*  100 


FIG.  12.— Computed  dates  when  the  chance  of  killing  frost  rises  to  1  in  10.    Before  these  dates 
killing  frost  will  occur  only  10  years  in  a  century. 

feature  of  this  map  is  the-  large  area  of  the  country  which  has  its  last  spring 
frost  rather  late  in  the  season. 
25807C-2— 17 3 


34 


PROCEEDINGS  SECOND  PAN   AMERICAN   SCIENTIFIC   CONGRESS. 


In  the  western  part  of  the  United  States — that  is,  west  of  the  front  range 
of  the  Rocky  Mountains — it  is  possible  to  draw  the  isochrones  only  for  the  1st 
of  each  month,  because  of  the  broken  topography  and  the  rapid  change  in 
frost  conditions  in  short  distances.  However,  it  has  been  possible  to  draw  these 
lines  with  one-month  intervals,  so  that  they  show  the  conditions  reasonably 
well.  A  great  portion  of  the  more  elevated  parts  of  the  country  are  subject 
to  late  spring  frosts.  Between  one-fourth  and  one-third  the  total  area  of 
the  United  States  is  probably  subject  to  June  frosts  in  half  the  years.  In 
the  western  portion  of  the  country,  except  in  favored  valleys  and  some  parts 
of  the  Southwest  late  frosts  are  the  rule.  In  the  eastern  part  of  the  United 
States  the  lines  of  killing  frost  dates  run  more  or  less  parallel  to  the  latitude 
line  showing  later  dates  with  increased  latitude  and  increased  distance  away 
from  bodies  of  water.  The  topography  in  the  East  is  not  of  such  marked 
importance  as  the  topography  in  the  West,  although  it  has  been  found  that 
even  the  lower  mountains  exert  a  very  considerable  influence.  The  average 


125  12O'          115  HO  1O5         1OO*         95  90  85  80  75  70'  65' 


FIG.  13.— Computed  length  of  available  growing  season  4  years  in  5. 

probable  error  of  the  average  dates  of  last  killing  frost  shown  by  the  map  is 
of  the  order  of  three  days,  that  is  about  one-third  the  interval  between  the 
isograms.  As  far  as  possible  the  lines  have  been  curved  to  include  all  stations 
and  in  most  cases  the  areas  between  the  lines  actually  represent  the  regions 
with  frost  dates  indicated  by  the  limiting  lines. 

There  is  some  question  as  to  whether  absolutely  uniform  records  will  give 
smooth  lines  with  broad  curves  and  fe\v  sharp  angles,  or  whether  even  the 
smoothest  topography  is  so  rough  that  local  air  currents  are  set  up  which  com- 
plicate the  conditions  so  that  smooth  lines  do  not  represent  the  actual  case. 
There  is,  of  course,  one  other  point  to  be  noted  about  the  isochronal  lines  of 
frost  occurrence,  and  that  is  that  these  lines  do  not  represent  anything  which 
actually  takes  place.  They  are  statistical  lines  resulting  from  the  accidental 
distribution  of  many  conditions,  and  this  accidental  distribution  tends  to  smooth 
out  irregularities.  The  way  in  which  frost  actually  occurs  may  be  shown  by 
figure  7,  which  is  a  map  of  the  conditions  in  Kansas  during  the  severe  spring 


ASTRONOMY,  METEOROLOGY,  AND  SEISMOLOGY.  35 

frosts  in  1907.  The  last  killing  frost  in  the  spring  of  1907  in  eastern  Kansas 
occurred  on  May  4.  The  area  in  which  this  occurred  is  limited  by  a  rather 
definite  line  which  is  shown  on  the  map.  The  last  killing  frost  in  a  strip  of 
varying  width  from  northeastern  to  south  central  Kansas  in  the  same  year 
occurred  on  May  15.  In  the  northeastern  half  of  the  State  the  last  killing 
frost  occurred  on  May  27.  There  was  no  gradation  between  these  areas.  The 
region  in  which  the  last  killing  frost  occurred  on  May  4  is  separated  from  that 
on  which  the  last  killing  frost  occurred  on  May  15  by  a  line,  and  the  same 
is  true  of  the  separation  between  this  region  and  that  where  the  last  killing 
frost  occurred  May  27. 

AVERAGE    DATES    OF    FIRST    KILLING    FROST    IN    FALL. 

Figure  9  shows  the  average  date  of  first  killing  frost  in  fall.  It  is  similar 
to  figure  8.  The  regions  which  are  not  subject  to  annual  frosts  are,  of  course, 
the  same  on  both  maps.  The  area  which  has  autumn  frost  before  September  1 
is  similar  to  that  having  spring  frost  after  June  1,  although  there  are  minor 
differences.  Perhaps  the  most  striking  thing  about  the  two  maps  is  their  great 
similarity. 

AVERAGE  SEASON  WITHOUT  KILLING  FROST. 

Figure  10  shows  the  average  number  of  days  between  the  last  killing  frost 
in  spring  and  the  first  killing  frost  in  fall.  This  has  sometimes  been  called  the 
"  growing  season,"  but  it  can  not  be  so  regarded  because  it  is  not  possible  in 
practice  to  make  use  of  the  whole  time,  owing  to  the  risk  involved  at  the 
beginning.  The  data  for  this  map  were  obtained  by  subtracting  the  average 
date  of  last  killing  frost  in  spring  from  that  of  first  killing  frost  in  fall  for  all 
Lhe  stations  available.  Isograms  have  been  drawn  for  10-day  intervals  in  the 
eastern  United  States,  and  for  30-day  intervals  in  the  western  United  States. 
The  length  of  the  season  varies  from  3G5  days  at  Key  West  to  considerably 
less  than  90  days  in  the  extreme  northern  portion  of  the  United  States  and  in 
the  higher  mountain  regions  of  the  West.  There  is,  of  course,  a  similarity 
between  this  map  and  the  maps  of  average  date  of  last  killing  frost  in  spring 
and  first  killing  frost  in  fall. 

A  striking  feature  of  this  map  is  the  large  area  of  the  United  States  in 
which  the  season  without  killing  frosts  is  90  days  or  less.  This  is  so  shoft 
that  ordinary  agriculture  is  largely  out  of  the  question,  and  only  hardy  grains 
and  grasses  can  be  cultivated  with  any  degree  of  assurance.  This,  of  course, 
does  not  mean  that  these  areas  are  waste,  because  in  very  many  cases  this 
is  the  region  in  which  the  most  important  forests  of  the  country  exist,  but 
these  regions  are  distinctly  outside  of  the  strictly  agricultural  area. 

DEVIATION    FROM    THE    AVERAGE    DATES. 

Although  it  has  not  been  possible  to  show  by  a  map  the  deviation  from 
average -dates  which  will  occur  at  varying  intervals,  maps  have  been  prepared 
which  show  the  dates  beyond  which  frost  is  a  probability1  in  only  1  year  in 
10  on  the  average.  Figure  11  shows  the  date  after  which  the  last  killing  frost 
in  spring  will  occur  in  1  year  in  10.  This  has  been  determined  by  multi- 
plying the  standard  deviation  for  569  stations  by  the  factor  1.28,  as  shown  in 


1  The  writer  wishes  to  record  his  obligation  to  Prof.  W.  J.  Spillman,  Chief  of  the  Office 
of  Farm  Management,  U.  S.  Department  of  Agriculture,  for  the  original  suggestion  of 
this  method  for  determining  frost  probability  and  for  advice  and  assistance  at  all  stages 
of  the  study. 


36  PROCEEDINGS  SECOND   PAN    AMERICAN    SCIENTIFIC   CONGRESS. 

Table  3,  and  adding  the  product  to  the  average  date.  For  example,  the  date 
after  which  a  killing  frost  at  Bismarck,  N.  Dak.,  in  1  year  in  10  on  the  average 
is  May  25.1  This  date  has  been  entered  on  the  map  for  Bismarck  and 
similar  dates  have  been  entered  for  each  station  for  which  the  standard  devia- 
tion has  been  determined.  This  map,  otherwise,  is  similar  to  the  map  of 
average  date  of  last  killing  frost  except,-  of  course,  that  the  number  of  stations 
used  is  much  smaller.  Figure  12  is  similar  to  figure  11 ;  it  shows  the  date 
before  which  the  first  killing  frost  in  fall  will  occur  1  year  in  10. 

PROBABLE   LENGTH    OF   THE    SEASON    WITHOUT    KILLING    FROST. 

Figure  13  shows  the  probable  length  of  the  season  without  killing  frost  in 
four  years  in  five.  This  has  been  determined  by  obtaining  the  difference 
between  the  date  shown  by  figure  11  and  that  shown  by  figure  12.  Strictly 
speaking,  this  map  shows  the  probable  length  of  the  season  without  killing 
frost  in  81  years  in  100,  but  the  probable  error  is  of  the  order  of  four  days, 
nnd  consequently  for  practical  purposes  it  is  sufficient  to  assume  that  the  map 
shows  the  season  for  four  years  in  five.  If  crops  are  in  a  condition  to  be 
injured  by  frosts  by  the  date  shown  in  figure  11,  1  crop  in  10  will  be 
injured  by  frost  in  the  spring.  If  the  crops  require  the  full  time  until  the 
date  shown  in  figure  12  to  mature,  and  are  subject  to  frost  damage  until  this 
date,  1  crop  in  every  10  which  survive  the  exceptional  spring  frost  will  be 
destroyed  in  the  fall.  This  may  be  stated  as  follows:  If  the  chances  of 
safety  in  the  spring  are  9/10  and  the  chances  of  safety  in  the  fall  are  9/10, 
then  the  chance  of  a  safe  growing  season  is  represented  by  the  product  of 
the  chances  of  safety  in  spring  and  the  chances  of  safety  in  fall.  Expressed 
mathematically  this  is  9/10X9/10=81/100,  which  is  the  probability  of  a 
frost-free  season  of  the  length  indicated  on  the  map. 

INFLUENCE   OF   TOPOGKAPHY    ON   FROST   DATES. 

The  influence  of  topography  on  frost  is  twofold.  In  the  first  place  higher 
altitudes  have  lower  temperatures  that  result  in  later  killing  frost  in  spring 
and  earlier  killing  frost  in  fall.  This  is  clearly  shown  on  the  maps  of  average 
dates  of  killing  frost.  The  second  influence  of  topography  depends  not  so 
much  on  altitude  above  sea  level  as  the  character  of  the  slope.  During  quiet 
nights  there  is  a  tendency  for  the  air  to  rearrange  itself  under  the  influence 
of  gravity.  This  is  particularly  noticeable  in  regions  of  broken  topography. 
While  the  mechanism  by  which  this  rearrangement  takes  place  is  complicated 
and  under  discussion  at  the  present  time,*  certain  phases  may  be  pointed  out. 

In  the  first  place  there  is  a  tendency  for  cold  air  to  collect  in  the  low  places, 
particularly  in  inclosed  valleys.  During  the  night  the  cold  builds  up  from  the 
bottom  of  the  valley  until  this  process  is  checked  by  the  morning  warming. 
There  is  also  a  tendency  for  the  chilled  air  to  flow  away  from  the  slopes. 
Whether  this  chilled  air  flows  down  the  hills  in  a  manner  similar  to  water, 
or  whether  there  is  a  complicated  exchange  of  air  from  the  hillsides  to  the 
air  over  the  valley,  is  still  under  discussion.  It  has  been  noted  in  many  regions 
that  there  is  a  warmer  belt  along  the  valley  sides — the  so-called  "thermal 
belt."  This  belt  has  frost  less  often  than  the  valley  bottoms  and  less  often 
than  the  hilltops  in  most  cases.  However,  where  the  hills  are  of  only  moderate 
height  it  sometimes  happens  that  the  hilltops  are  included  within  the  thermal 
belt.  Practical  application  of  the  influence  of  topography  on  frost  may  be 

1  See  Table  4  for  the  method  by  which  this  date  is  obtained. 

*  See  McAdie,  A.  G.  :  Temperature  inversions  in  relation  to  frost.  Harvard  College 
Observatory  Annals,  73 :  168-177,  Cambridge,  1915 ;  and  Marvin,  C.  F. :  Air  drainage 
explained,  [U.  S.]  Monthly  Weather  Review,  42:583-585,  Washington,  1915. 


ASTBONOMY,   METEOROLOGY,  AND  SEISMOLOGY.  37 

seen  in  the  occurrence  of  places  which  are  particularly  subject  to  frost  damage 
or  are  particularly  frost  free.  The  relations  of  "air  drainage"  are  probably 
responsible  for  the  well-known  spottedness  of  frost  occurrence.  Slight  dif- 
ferences of  elevation  make  possible  the  movement  of  air  under  the  influence 
of  gravity  during  the  calm  of  the  typical  frost  night.  The  .whole  problem 
is  one  of  a  very  nice  adjustment  of  conditions  and  can  not  be  dealt  with  in  a 
general  way,  although  in  determining  the  liability  to  frost  of  particular  portions 
of  small  regions  the  influence  of  "air  drainage"  becomes  of  enormous  im- 
portance. 

No  careful  attempt  has  yet  been  made,  largely  because  of  lack  of  available 
data,  to  determine  just  what  is  the  relation  between  altitude  and  topography. 
It  has  been  suggested  that  a  canyon  approximately  500  feet  deep  in  central 
Washington  will  be  colder  at  the  bottom  than  at  the  canyon  rim.  If  the  depth 
is  greater  than  500  feet  the  altitude  effect  usually  makes  the  canyon  rim  more 
frosty  than  the  bottom  of  the  canyon.  In  general  it  may  be  sufficient  to  say 
that  very  considerable  portions  of  the  western  United  States  are  subject  to 
early  and  late  frosts  because  of  their  altitude  above  sea  level,  and  that  the 
exact  occurrence  of  frost  locally  in  a  broken  region  is  dependent  upon  the 
topography,  the  most  frost-free  places  being  the  valley  sides,  especially  the 
slopes  of  alluvial  fans  extending  into  the  valleys.  There  are  also  areas  which 
are  subject  to  cold  air  drainage,  particularly  areas  opposite  canyon  mouths 
from  which  a  stream  of  cold  air  flows,  making  these  subject  to  frosts  when 
other  portions  of  the  valley  do  not  reach  such  low  temperatures. 

The  whole  question  of  topography  and  frost  is  one  which  needs  a  great  deal 
more  study,  and  work  similar  to  that  now  being  carried  on  by  Cox  in  North 
Carolina  should  be  extended  to  all  parts  of  the  country.  An  example  of  the 
commercial  value  of  these  studies  is  to  be  found  in  the  work  done  in  southern 
California  near  Pomona  and  in  the  Corona  district.1 

THE    RELATION     BETWEEN     DATES     OF    LAST    KILLING    FBO8T    IN     SPEING    AND    FIRST 

KILLING    FROST    IN    FALL. 

In  the  study  of  frost  dates  it  appears  that  the  last  spring  frost  and  the  first 
full  frost  could  not  be  regarded  as  entirely  independent  of  each  other.  From 
a  theoretical  consideration  it  seems  wholly  possible,  if  not  probable,  that  the 
low  temperature  conditions  resulting  in  late  spring  frost  might  extend  through 
the  summer  and  give  earlier  fall  frosts,  or  that  the  higher  temperatures  re- 
sulting in  an  early  date  of  last  spring  frost  might  also  affect  the  first  fall 
frost.  In  the  attempt  to  determine  the  probable  length  of  the  season  without 
killing  frost  in  9  years  in  10 — that  is,  to  determine  the  business  risk  in  the 
same  manner  as  for  the  last  spring  and  the  first  fall  frost — a  slight  but 
constant  relation  was  found.  Coefficients  of  correlation2  between  spring  and 
fall  frost  were  determined  for  several  stations.  In  nearly  all  the  cases  con- 
sidered there  is  a  coefficient  of  correlation  of  between  —  0.10  and  —  0.30  with 
a  probable  error  of  something  less  than  half  this  amount.  Correlation  is 
not  regarded  as  well  established  unless  the  coefficient  of  correlation  is  equal 
to  six  times  the  probable  error  of  the  coefficient,  but  there  is  here  a  condition 


1  See  Carpenter,  F.  A. :  Utilization  of  frost  warnings  in  the  citrus  region  near  Los 
Angeles,  Cal.,  [U.  S.]  Monthly  Weather  Review,  42  :  569-571,  Washington,  1914.  Garth- 
waite,  J.  W. :  Letter  on  frost  and  frost  prevention,  [U.  S.]  Monthly  Weather  Review, 
42  :  571-572,  Washington,  1914.  Carpenter,  F.  A.,  and  Garthwaite,  J.  W. :  Memorandum 
on  air  drainage  in  the  vicinity  of  the  Corona  district,  California,  [U.  S.]  Monthly 
Weather  Review,  42  :  572-573,  Washington,  1914. 

*  See  Yule,  G.  Udny  :  An  introduction  to  the  theory  of  statistics  ;  London,  C.  Griffin 
&  Co.,  1912,  pp.  157-253.  Davenport,  C.  B. :  Statistical  methods;  New  York,  Wiley, 
ed.  3,  1914,  pp.  42-61.  [Great  Britain]  Meteorological  Office:  The  computer's  handbook, 
section  5,  London,  1915. 


38  PROCEEDINGS  SECOND  PAN   AMERICAN   SCIENTIFIC   CONGRESS. 

in  which  the  slight  correlation  always  leans  in  the  same  direction.  In  the 
very  small  number  of  cases  in  which  there  is  positively  correlation,  the  coeffi- 
cient of  correlation  is  less  than  0.10,  and  its  probable  error  has  practically 
the  same  value.  This  means  that  zero  is  as  likely  as  the  value  of  the  coefficient 
as  the  value  determined.  Without  going  into  the  matter  in  detail,  the  indica- 
tions are  that  if  the  last  killing  frost  in  spring  is  late,  there  is  a  tendency  for 
the  first  killing  frost  in  fall  to  be  early,  and  if  the  last  killing  frost  in  spring 
is  early,  there  is  a  tendency  for  the  first  killing  frost  in  fall  to  be  late.  How- 
ever, the  records  are  not  complete  enough,  nor  is  the  correlation  well  enough 
marked  for  individual  stations  to  make  this  more  than  a  probability.  This 
condition,  however,  opens  an  interesting  field  for  study  which  should  be  pur- 
sued further.1 

PROTECTION  AGAINST  DAMAGE  BY  FROST. 

Fruits  and  vegetables  are  now  successfully  protected  in  many  parts  of 
the  United  States,  and  equipment  for  frost  fighting  is  regarded  as  necessary 
in  all  the  important  fruit  regions.  Protection  against  frost  damage  has  been 
accomplished  mainly  by  the  use  of  small  fires,  which  keep  the  tempera tur*» 
above  the  dangerous  point  by  supplying  heat  to  the  low  area  to  make  up 
for  the  loss  to  space  by  radiation.  Usually  there  is  a  good  deal  of  smoke 
together  with  the  heat,  so  that  radiation  of  heat  from  the  earth  is  somewhat 
checked.  Various  other  methods  have  been  used  to  prevent  occurrence  of 
freezing  temperatures  under  the  local  radiation  conditions  which  result  in 
hoar  and  black  frosts.  During  the  general  freeze  condition  attempts  to 
protect  against  frost  damage  have  not  been  so  successful.8 

CONCLUSION. 

The  maps  presented  represent  in  the  first  place  the  average  conditions  of 
frost  and  season  without  killing  frost  which  exist  in  the  United  States. 
They  have  been  drawn  on  a  basis  of  all  available  data,  included  first  and  fore- 
most, the  frost  dates  recorded  by  the  observers  of  the  United  States  Weather 
Bureau,  and,  secondly,  topographic  and  botanic  data  obtained  from  various 
sources. 

The  maps  showing  probable  occurrence  of  last  killing  frost  in  spring  and 
first  killing  frost  in  fall  in  one  year  in  ten  are  new,  and  show  more  clearly 
than  the  others  the  business  risk  involved  in  planting  and  harvesting  at 
particular  times.  The  map  of  probable  length  of  the  season  without  killing 
frost  in  four  years  out  of  five  shows  what  time  is  available  for  the  growth 
of  crops  in  the  different  parts  of  the  United  States  with  a  loss  of  only  one- 
fifth  of  all  crops  from  frost,  which  may  be  assumed  as  a  fair  business  risk. 
This  map  and  the  data  upon  which  it  is  based  show  better  than  any  maps 
previously  prepared  the  existence  of  killing  frost  as  a  limiting  factor  for 
crops.  It  does  not,  however,  show  the  heat  supply  upon  which  the  crop 
depends  for  its  growth.  The  frost  problem  for  most  crops  in  the  United 
States,  from  an  agricultural  point  of  view,  is  that  of  determining  the  proba- 
bility of  frost  and  the  risk  involved  in  planting  at  different  times.  The  cost 
of  protection  against  frost  damage  is  so  great  that  it  does  not  apply  to  the 
staple  crops  of  the  country.  The  problem  for  the  farmer  is  to  determine  the 
frost  conditions  he  will  have  to  meet  and  to  arrange  his  crops  and  his  agri- 
cultural practice  with  reference  to  these  frost  conditions. 

1  See  Reed,  W.  G. :  The  probable  growing  season,  [U.  S.]  Monthly  Weather  Review, 
44  :  509-512,  Washington,  1916. 

8  Protection  against  damage  by  frost  is  discusseg  in  the  [U.  S.]  Monthly  Weather 
Review,  42:562-592  (October,  1914),  and  in  Better  Fruit  (Hood  River,  Oreg.),  5  :  no.  4 
(October,  1910).  See  also  Reed,  W.  G. :  Protection  from  damage  by  frost,  Geographical 
Review,  1 : 110-122,  New  York,  1916. 

O 


14  DAY  USE 

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LD  21A-50m-8,'57 
(C8481slO)476B 


General  Library 

University  of  California 

Berkeley 


Binder 
Gaylord  Bros. 

Makers 
Syracuse,  N.  Y. 

PAT.  JAN  21,  1908 


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UNIVERSITY  OF  CALIFORNIA  LIBRAR 


